Singleplayer world is crashing

[KidWithAPc]

Ok so, i've tried everything, i've allocated more ram, removed more ram, redownloaded Tekkit Classic and the launcher, but nothing works. Everytime i load up my singleplayer world that has a ton of progress on it, i see one frame of the world and it's barely loaded (it's mostly snow particles) and i can hear the ambiance, but the lag is so bad i can't move at ALL.

 

Please halp.