Being who I am, I gave up on having the dealer acknowledge that my heaters were garbage. I ordered replacement elements for both seats. Yes, GM did change the part numbers for both elements.
Assuming replacing the elements works, I'll post a write up for those who may want to do the same.
I've already had the passenger seat out and partially apart once. It isn't fun releasing the upholstery from the bottom of the seats.
2015 Colorado Ext. Cab Z71 4X4 (4/15 build date):
Bose, nav., sliding rear window, factory spray-in bed liner, fender guards, Rallyarmor UR mudflaps, Truxedo Lo Pro QT, door sill protectors, BNR tune.