Game slows down when facing left

[Vampirel]

Hello, I am working on Bleach LF2 modification and as title says, due to its large sprites it slows down when going or casting moves to left. It depends on user's Pc though, as I was getting reports; some do have these problems and some don't. Though the version is still in like half of progress I am afraid that it will one day stop completely. Any solution to all this?