ERAT340 -- no rubbing on the front edges of the fenders, nor upper lips (rolled lips and slightly pulled... but again, I've got a stiff suspension, so, hardly any dipping at all.... even considering that my car is lowered f/r.
My fenders are slightly modified to accommodate 16x10 rims (5" back spacing... pushing the tires out towards the fenders ~1/2" from a stock dimension setup) with 275-45-16 DOT Hoosiers A6 race autocross tires.... no rubbing and just enough clearance.
If you'd use correct offset/backspacing, then the 255-60-15 will work without any problems, nor any need to modify the fender (again, tucking the lips for additional insurance would be the most needed to do).
One thing, perhaps with most wider tires, or taller tires, too, is the front rear inside will rub slightly against the frame rail when turned to a lock... no big deal.. just a bit of rub.