Need tire advise

[GBGN1]

Ive got 15/7 with 3 1/2 backing on front and 15 /8 on back withe the same backspaceing\

Im putting NITTOs on the back of the car and want to know the best size for the rear with the most meat.I was thinking of running a 255-60-15 can i go bigger?

Thanks Brian

What would be the best size for the front too