Measure the clearance to the wheel lip you have now and subtract 0.5". That's pretty much where your new combo would land.
A 15 x 7 w/ 4" bs would put the wheel in the same position as the 15 x 8 w 4.5" bs you have now. So, by going with 3.5" bs on the 15 x 7, you're essentially moving the wheel and tire outward by 0.5".
confusing but I'll take your word for it. If that's the case , they won't fit and I won't grab them. Thank you. Just trying to figure out where the other half inch disappeared to lol