you should be able to run 215s with out much problem its basically like puting 235 on 1*x7.5 but or 245 on1*x8.0 225 is to high tho.
6.5= 215/205/195
7.0=225/215/205
7.5=235/225/215
etc..... the middle number is a,ways the best but you can go up a size or down but never go up 2 sizes or down 2