You planning on keeping the spacers with the new set? Feel like since they're the same width it shouldn't be too much different except for the height. What tire size do you have on the 15x8? Might rub with the 50 profile though since 2 inches kinda make a difference.

 

I've got 17x8 +38s on my car. Had to have the rears rolled. The 15's didn't require rolling? I'm surprised. But the 17's should fit fine.