Crash report:

 

---- Minecraft Crash Report ----
// Why did you do that?

Time: 4/27/20 12:40 PM
Description: Exception in server tick loop

java.lang.NoSuchMethodError: net.minecraftforge.event.ForgeEventFactory.fireChunkWatch(ZZLnet/minecraft/entity/player/ServerPlayerEntity;Lnet/minecraft/util/math/ChunkPos;Lnet/minecraft/world/server/ServerWorld;)V
    at net.minecraft.world.server.ChunkManager.handler$zbn000$inject$setChunkLoadedAtClient$0(ChunkManager.java:1556) ~[?:?] {re:mixin,re:classloading,xf:OptiFine:default,pl:mixin:APP:mixins.optiforge.json:net.minecraft.world.server.MixinChunkManager,pl:mixin:A}
    at net.minecraft.world.server.ChunkManager.func_219199_a(ChunkManager.java:909) ~[?:?] {re:mixin,re:classloading,xf:OptiFine:default,pl:mixin:APP:mixins.optiforge.json:net.minecraft.world.server.MixinChunkManager,pl:mixin:A}
    at net.minecraft.world.server.ChunkManager.func_219234_a(ChunkManager.java:1050) ~[?:?] {re:mixin,re:classloading,xf:OptiFine:default,pl:mixin:APP:mixins.optiforge.json:net.minecraft.world.server.MixinChunkManager,pl:mixin:A}
    at net.minecraft.world.server.ChunkManager.func_219210_a(ChunkManager.java:1203) ~[?:?] {re:mixin,re:classloading,xf:OptiFine:default,pl:mixin:APP:mixins.optiforge.json:net.minecraft.world.server.MixinChunkManager,pl:mixin:A}
    at net.minecraft.world.server.ServerChunkProvider.func_217230_c(SourceFile:489) ~[?:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.world.server.ServerWorld.func_217465_m(ServerWorld.java:987) ~[?:?] {re:classloading}
    at net.minecraft.world.server.ServerWorld.func_217448_f(ServerWorld.java:886) ~[?:?] {re:classloading}
    at net.minecraft.world.server.ServerWorld.func_217435_c(ServerWorld.java:863) ~[?:?] {re:classloading}
    at net.minecraft.server.management.PlayerList.func_72355_a(PlayerList.java:167) ~[?:?] {re:classloading}
    at net.minecraft.network.login.ServerLoginNetHandler.func_147326_c(ServerLoginNetHandler.java:116) ~[?:?] {re:classloading}
    at net.minecraft.network.login.ServerLoginNetHandler.func_73660_a(ServerLoginNetHandler.java:63) ~[?:?] {re:classloading}
    at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:224) ~[?:?] {re:classloading}
    at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:135) ~[?:?] {re:classloading}
    at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:864) ~[?:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:782) ~[?:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:163) ~[?:?] {re:classloading,xf:OptiFine:default}
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:635) [?:?] {re:classloading,pl:accesstransformer:B}
    at java.lang.Thread.run(Thread.java:745) [?:1.8.0_51] {}

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- System Details --
Details:
    Minecraft Version: 1.15.2
    Minecraft Version ID: 1.15.2
    Operating System: Windows 10 (amd64) version 10.0
    Java Version: 1.8.0_51, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 958692464 bytes (914 MB) / 2147483648 bytes (2048 MB) up to 2147483648 bytes (2048 MB)
    CPUs: 8
    JVM Flags: 9 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xss1M -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
    ModLauncher: 5.0.0-milestone.4+67+b1a340b
    ModLauncher launch target: fmlclient
    ModLauncher naming: srg
    ModLauncher services: 
        /eventbus-2.0.0-milestone.1-service.jar eventbus PLUGINSERVICE 
        /forge-1.15.2-31.1.0.jar object_holder_definalize PLUGINSERVICE 
        /forge-1.15.2-31.1.0.jar runtime_enum_extender PLUGINSERVICE 
        /accesstransformers-2.0.0-milestone.1-shadowed.jar accesstransformer PLUGINSERVICE 
        /forge-1.15.2-31.1.0.jar capability_inject_definalize PLUGINSERVICE 
        /forge-1.15.2-31.1.0.jar runtimedistcleaner PLUGINSERVICE 
        /preview_OptiFine_1.15.2_HD_U_G1_pre8.jar OptiFine TRANSFORMATIONSERVICE 
        /forge-1.15.2-31.1.0.jar fml TRANSFORMATIONSERVICE 
        /Fermion-Lib-1.15.2.jar fermion.asm.service TRANSFORMATIONSERVICE 
        /MixinBootstrap-1.15.2.jar mixinbootstrap TRANSFORMATIONSERVICE 
        /MixinBootstrap-1.15.2.jar mixin PLUGINSERVICE 
        /MixinBootstrap-1.15.2.jar mixinbootstrap PLUGINSERVICE 
    FML: 31.1
    Forge: net.minecraftforge:31.1.0
    FML Language Providers: 
        [email protected]
        minecraft@1
    Mod List: 
        Fermion Fermion ASM Service {[email protected] NONE}
        Fermion Fermion Companion {[email protected] NONE}
        Fermion Fermion Test Suite {[email protected] NONE}
        forge-1.15.2-31.1.0-client.jar Minecraft {[email protected] DONE}
        __extraction__fermion_extraction__mod_file_Fermion_mod.jar Fermion {[email protected] DONE}
        CyclopsCore-1.15.2.jar Cyclops Core {[email protected] DONE}
        Simply-Tea-Mod-1.15.2.jar Simply Tea {[email protected] DONE}
        Double-Doors-Mod-1.15.2.jar Double Doors {[email protected] DONE}
        Just-Mob-Heads-Mod-1.15.2.jar Just Mob Heads {[email protected] DONE}
        Nimble-Mod-1.15.2.jar Nimble {nimble@NONE DONE}
        No-Hostiles-Around-Campfire-Mod-1.15.2.jar No Hostiles Around Campfire {[email protected] DONE}
        OptiForge-Mod-1.15.2.jar OptiForge {[email protected] DONE}
        Moving-Elevators-Mod-1.15.2.jar Moving Elevators {[email protected] DONE}
        Everlasting-Abilities-Mod-1.15.2.jar EverlastingAbilities {[email protected] DONE}
        Easy-Elytra-Takeoff-Mod-1.15.2.jar Easy Elytra Takeoff {[email protected] DONE}
        forge-1.15.2-31.1.0-universal.jar Forge {[email protected] DONE}
        Named-Areas-Mod-1.15.2.jar Named Areas {[email protected] DONE}
        FastLeafDecay-Mod-1.15.2.jar FastLeafDecay {fastleafdecay@v20 DONE}
        Healing-Campfire-Mod-1.15.2.jar Healing Campfire {[email protected] DONE}
        Bambootiful-Mod-1.15.2.jar Bambootiful {[email protected] DONE}
        JourneyMap-Mod-1.15.2-Unlimited.jar Journeymap {[email protected] DONE}
    Player Count: 1 / 8; [ServerPlayerEntity['DeeShep'/243, l='Adventure Begins', x=-13.50, y=63.00, z=-57.50]]
    Data Packs: vanilla, mod:bambootiful (incompatible), mod:cyclopscore (incompatible), mod:doubledoors (incompatible), mod:easyelytrato (incompatible), mod:everlastingabilities (incompatible), mod:fastleafdecay, mod:fermion (incompatible), mod:fermion.asm (incompatible), mod:fermion.asm.service (incompatible), mod:fermion.asm.test (incompatible), mod:forge (incompatible), mod:healingcf (incompatible), mod:jmh (incompatible), mod:journeymap (incompatible), mod:movingelevators, mod:nhacampfire (incompatible), mod:nimble, mod:nmdar (incompatible), mod:optiforge, mod:simplytea (incompatible)
    Type: Integrated Server (map_client.txt)
    Is Modded: Definitely; Client brand changed to 'forge'
    OptiFine Version: OptiFine_1.15.2_HD_U_G1_pre8
    OptiFine Build: 20200222-224902
    Render Distance Chunks: 15
    Mipmaps: 4
    Anisotropic Filtering: 1
    Antialiasing: 0
    Multitexture: false
    Shaders: null
    OpenGlVersion: 4.6.0 - Build 26.20.100.7262
    OpenGlRenderer: Intel(R) HD Graphics 630
    OpenGlVendor: Intel
    CpuCount: 8

Try removing Optifine.

Where did you get your Optifine, anyway? I don't even see that version on their download page.

Make sure you read the changelog for any version of Optifine you download, it will specify which version, if any, of forge that it works with.

" OptiFine Version: OptiFine_1.15.2_HD_U_G1_pre8" it is this one. There is a mod which claims that it can make optifine 1.15+ compatible with Forge.

When I removed that mod and optifine, it started to work, thank you. Do you have any idea how can I make optifine 1.15.2 and Forge compatible?

They were from 9minecraft.net. Thanks to you, I learnt that this site is not trusted and does not credit modders. Right now, I am installing modpacks from curseforge.com. Ignorance is bliss...

34 minutes ago, Ugdhar said:

Try removing Optifine.

Where did you get your Optifine, anyway? I don't even see that version on their download page.

Make sure you read the changelog for any version of Optifine you download, it will specify which version, if any, of forge that it works with.

Yeah, you are right. It was from 9minecraft site. It is not even legit

5 minutes ago, NewbieSurvivor said:

Yeah, you are right. It was from 9minecraft site. It is not even legit

Make sure you delete any mods you downloaded from there, and redownload from a good site such as curseforge.com.

The link diesieben07 shared will give you a list of ones to avoid, I think they even have a browser extension that will warn you if you accidentally go to one.

You never know what could be hidden in those .jar files downloaded from sketchy places!!!!

I redownloaded every mod I did download from that site. The site I used is curseforge.com. Thanks for the help guys. I am going to scan my computer for any malwares.