Im I right or not please correct me

It makes sense to me but I might be wrong. It seems like a 15x8 rim with t less back spacing you have and the more offset you have you wont rub as much. Also, with a 15x8 rim that has 4" backspace and less offset you will rub more cause you will rub on frame and etc.

 

since you're referencing 15s, i assume you are talking about a first gen 6 lug?

as for rub, a lower backspace will help keep the inner sidewall of the tire from rubbing on the frame and stock upper control arm, but if on stock suspension, the outer corners can end up rubbing on the pinch weld, fender flares, and front bumper valance...