Tire clearance

I'd measure how much room you've got now with the current combo. That'll tell you pretty quickly whether 255/60s will work with the 8" wheel. The 255/60/15 will be about 1/2" wider at the tread on each side and 5/8" wider in the section on each side than what you've got now. Check section clearance to the spring and inner and outer wheelhouse. That tire's a tad taller too so see how much room you've got at the front arch lip.