The only 15" tire I saw was a 165/80R15 which is way too narrow for a GMC Jimmy. It should take a 235/75R15. A much wider and taller tire overall. Take a look at the Goodyear Wrangler Trailrunner AT. Nice on/off road tire with a decently chunky offroad pattern but still really does well and rides quiet on the highway. But not insanely expensive.

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