Hi, I know this is an older thread, but I have always experienced the exact same problem with my 2015 Trailhawk, from day 1. Did you ever get this problem resolved? It's so annoying that my relatively new vehicle with high end electronics has a heater that doesn't work as well as any car I have ever owned, dating back 40 years ago!
Sorry to hear about this! If you decide to visit your local dealership I'd be happy to follow up with them for you if needed. Just PM our page with your VIN and let me know.
Jeep Social Care Specialist