I tried to play. FPS was terrible. I added optifine, betterfps, disabled betterfoliage, replaced nei with the nei version for the GTNH modpack, and singleplayer was then able to achieve fps around 50 instead of 15, except when loading new chunks.
Logged onto the server and my fps inexplicably was tanked in spite of the changes I made.
Proctor was on and suggested increasing ram. I upped it from 4 gigs to 8. no change.
Maybe something about the area I spawned in, even though the singleplayer biome i spawned in was also very heavily forested. idk.