More durable 15" tires

[1976gmc20]

Is there a 15" tire that will hold up better to damage than a LT235/75R15 (C rating) on gravel roads under a Square Body Suburban ???

We get often non-repairable rock damage by the time the tires are 50% or sometimes even sooner. They don't seem to make a D or E tire for 15 inch wheels. We don't even "off-road" but we live out on poorly maintained gravel and dirt roads. I don't remember having these kind of problems years ago with bias ply tires, but the radials seem very "weak" by comparison.

This outfit isn't lifted and never will be, but there is plenty of fender clearance. I'm wondering if a somewhat larger tire could be had in heavier ply rating or if it would just hold up better because it's bigger, or if it would just be more expensive to replace?

We put a new set of tires on the Suburban a couple years ago and have hardly driven it since, but we got a Jeep XJ this spring and I was wondering if it would be a good idea to put some bigger tires on the Suburban and swap the near new LT235/75R15s to the jeep?