This is only happening when I have optifine added. also this version of optifine worked before the recent update. Is there some other mods that's not cooperating with it?
Since the pack was updated, Optifine now causes the client to crash, Done - Crashing after update | MineYourMind Community Until someone finds a fix for this, your best bet would be to play without it.
Maybe some other FPS performance enhancing mods might work, it might be worth a try to use some other ones if your running at 15FPS, best of luck!
Tinker a bit with graphics card settings, used to get 100+ fps with optifine, now 80+ fps with optimized graphics card. Not too bad, I think.