15x8 w/3.75" backspace question

You didn't mention offset which affects the fit and appearance, too. Assuming its a "zero" offset, I'm betting you're good with the 15x8 fit in the the rear fender well. A 4" or 4.25" backspace is better. The appearance may be a little "pushed out" but you'll have to mount them to see the look and decide if it's what you want.