Extreme Worldgen lag without any mods.

Hi!

Im trying to host a Forge 1.12.2 minecraft server, the problem is that whithout any gamechanging mods the server TPS drops from 20 to 3 in arround 1-5 seconds of flying in spectator at max speed.

The only mods that i have are LagGoggles and Something that messes with the TAB. [Screenshot]

The problem is that even there are low tps forge isnt taking more cpu? Minecraft does not support multithread right? Well, none of my cores are +15% of charge while running the server, its something with forge that isnt taking resources because im able to support an spigot/paper server whith more than 50 plugins (mods are heavier, but remember i have 2) that stays between 19-20 tps while 3 players are flying with the spectator at max speed.

Bat file:

java -Xms8G -Xmx8G -jar forge.jar nogui
pause

I have tried whith this 

 -XX:+UnlockExperimentalVMOptions -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M

but i couldnt tell the difference.

My PC specs:

Ryzen 5 3600 

16 Gb DDR4 3200Mhz 

Server running in SSD.

I dont know whats causing that, but its clearly impossible to play.