In the games code, go into "script/th_bsm/lib/zakolib/lib_zakodraw.dnh" (you can open dnh files with notepad). At line 291, there should be a function that says "DrawFamiliarHitodama". Put "//" in front of that function. That should drastically reduce the lag on Nezu, though her familiars won't have the little fire trails on them.
Still trying to figure out a way to reduce lag on Fuuma. Think it has something to do with the lasers, but I have no idea what about the lasers would be causing so much. I can let you know if I find a fix.