You won't know until ya try it. It's a trainer and your not going to get much more performance out of it no matter what. Ya want more perfomance build another wing which basically means build another plane. If it was a more symmetrical wing playing with the incidence might improve something.
My hypothesis in your trainer is it'll increase the the take off and landing speed. What is the plane doing that you feel the need for the change? Is it just a geewiz or is it doing something you don't like? Of it's just a geewiz thing I's start out incrementally. Say take out a half degree and see what happens then 1 and so on.