I've got a 15 that hasn't been the best ownership experience, but speaking for myself, and the guys on the ColoradoFans forum, I haven't heard of any timing chain issues. The prevalent issues I keep seeing on the forum, and on my truck, are transmission programming on the 3.6 / 6-speed auto, longevity and durability of the Diesel engine (a few let go for no apparent reason), a noisy front seal on the transfer case, defective leather seat covers, rough idle on the 3.6, hood flutter, and shuddering in the newer 8-speed autos.
I've had the driver's seat cover replaced under warranty, several recalls performed while it was there, the front seal in the transfer case replaced twice in 40,000 miles for a loud squeak, and most recently had the "chugging" issue fixed with the 6-speed transmission programming, which despite being a TSB for the 2015s, having been released in May 2018, they charged me for it because I was beyond 3/36. IMO, that fix should've been free, as it was a programming issue that existed since the build date.
I went ahead and bought a new bottom seat cover for the driver's seat a few weeks ago in an anticipation of a re-occurrence of the side cracking, while they're still available from GM. I found out the hard way with my '05 Sport Trac that if you wait to long to order certain trim items (seat cushions, in this case), they go out of production and are impossible to find new.
It's a nice truck and overall not a regrettable purchase, but GM could've done some things better.