I( would normally refer you to the REMCO website, but it does not list the 2015 GMC, and does not have the 1500 listed as a 2014 model.
Therefore, I can only recommend that you read the Owners Manual under "Recreational Towing", if such a section exists.
If a driveshaft disconnect system is not available for that particular year and model, then you are quite possibly back to the trailer, or getting under it to remove the driveshaft from the differential yoke and tieing it up out of the way. I used to do that with a Datsun pickup, it isn't all THAT hard!
CM1, USN (RET)
2017 Jayco TT
Daily Driver: '14 Subaru Outback
1998 Dodge QC LWB, Cummins, 5 speed, 4X2
2 Kawasaki Brute Force 750 ATVs.
Pride Raptor 3 wheeled off-road capable mobility scooter
"When seconds count, help is only minutes away!"