20x9.5 offset question for my '70 fleet with wide axle

[Harrison.]

I ordered a set of 20x8 and 20x9.5 rev 100 classics for my 1970 fleetside C10. When I ordered I went with a 0mm offset on the rears but was just emailed by the seller telling me they were back ordered and that +15mm were ready to ship. I know it's only about half an inch, but that would be half inch further IN the wheel tub, correct? Anyone else running this offset? How would it look? I was already worried I would have to run a spacer in the rear to bring the wheel out to the edge of the fender. Oh and the truck has a 5/4 drop. Thanks.