You can look up the manufacturer’s recommendations on rim sizes. BF Goodrich says a 15x8” is the minimum. If it wasn’t safe, they wouldn’t list it as the minimum. In today’s world of lawyers and lawsuits I’d say that’s a safe recommendation, they wouldn’t hang themselves out for a lawsuit.
Tread width on those tires is listed as 10”. An 8” rim is actually 9” wide outside lip to outside lip, so you’re talking a 1/2” of tread on either side. The section width is 12.2”, but that’s measured on a 15x9.5” so they won’t be that wide on a 15x8. The tread will end up rounded across the tread profile at the normal recommended tire pressure. So you’ll have to lower the tire pressure to get a nice tread pattern.
