[b454rat]

It's been a while, but the 15s I have have at least 4" b/s. The rear is from a 1 ton van, has the huge breaks, and it's close but they clear. I had a set with 4.25" on a 1 ton rear, still cleared. Only issues I've ever had with 15s is clearing a 3/4 front and a 1 ton, but grinding takes care of that.

15" rims have more tire options not to mention cheaper. If you need more capacity, then might have to go with 16s or bigger. But IMO, bigger doesn't always look better, especially on the 70s/80s trucks.