There were two active recalls on the 15 Yukon XL, one involved the sticker id'ing the fuses in the driver's side dash fuse block. The sticker (which was probably replaced by the owner, as they were sent out to owners to do themselves), the other (and it's one I still need to bring my into the dealer for, though I've never had the issue) is the "Slow speed maneuvering issue", in which vehicles equipped with the "auto park" have had their steering fail momentarily while turning at slow speeds (parking). I would imagine you've run the vin to see what (if any) outstanding recalls are (if any) still outstanding.
I'm with others here in that's pretty high mileage, if they've been diligent in their care (with all of the paperwork to show) then maybe- but then again, mine has 11,566 miles on it-
This may help as well:
https://www-odi.nhtsa.dot.gov/owner...a.model=YUKON&searchCriteria.prod_ids=1971434