I need help, my forge server wont run with enough ram for a mod pack I'm using.

Ok so I have a server that my dad got from his work for free, its like 10 years old or smt but it works and it has lots of ram and 12 cores which for a minecraft server thats great, I have windows installed on the server and i have ran minecraft servers on it in the past with my friends and it worked fine but I tried the kinda crazy craft mod pack on curseforge  and I dont everything I had too and i have all the files but when I open the run.bat file this message comes up :

C:\Users\Gamer\Desktop\KindaCrazyCraftServer1.15.1 (2)\server>java -Xmx30G -jar forge_server.jar nogui
A problem occurred running the Server launcher.java.lang.reflect.InvocationTargetException
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:110)
        at java.base/java.lang.reflect.Method.invoke(Method.java:577)
        at cpw.mods.fml.relauncher.ServerLaunchWrapper.run(ServerLaunchWrapper.java:43)
        at cpw.mods.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:12)
Caused by: java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and java.net.URLClassLoader are in module java.base of loader 'bootstrap')
        at net.minecraft.launchwrapper.Launch.<init>(Launch.java:34)
        at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
        ... 3 more

C:\Users\Gamer\Desktop\KindaCrazyCraftServer1.15.1 (2)\server>pause
Press any key to continue . . .

Ive remade the server several times i downloaded old java versions because its a 1.7.10 server so i figured it might need a old java but that didnt work, I also tried jartex and that didnt work either, when i run it as administrator it says :

C:\Windows\system32>java -Xmx30G -jar forge_server.jar nogui
Error: Unable to access jarfile forge_server.jar

C:\Windows\system32>pause
Press any key to continue . . .

when I run open the forge_server.jar file it opens up but it only uses 4gb of ram and for 6 people and a modpack that its enough and it barley runs, and has so much delay, I dont know how to fix this can someone help me out here?