A little more drastic work-around...
You could run 5 1/4” backspacing and run a 1” spacer or a 2” overall wider rear end.
Wheel will look like a 15x7 from the side.
That's what I did. I ordered 15x8 rallyes from Stockton Wheel in CA with 1" more backspacing than a stock 15x7. IIRC it was 5-1/4" like autoxcuda stated. I also moved my springs inboard about 3/4" per side for clearance. This gave the correct fit for the trim ring with no gap and the outside of the tire and wheel are in the stock location with a stock width rear housing.
