I don't know I will try but other modpacks have the same thing not just the pixelmon one.
Bteam plays a bit better but still has a little lag but not as bad as the pixelmon one.
I tried Tekkit legends and it didn't run smoothly at all a lot worse than Bteam.
updated log
http://paste.ubuntu.com/23079641/plain/
Every modpack is really laggy even when I am on the starting screen. Some of the modpacks with only two or three mods work okay but still gets a few lag spikes.Vanilla works perfectly fine no lag at all. Also this has not been like this forever I was able to play modded minecraft just fine before and all of a sudden it would not work it is unbearable to play with only a few FPS. I have allocated 3Gb RAM and other modpack launchers have the same problem.