Don't know about the 2015 but I ordered my previous 2001 Chevy 2500HD with that option. IIRC it was located secured to the wiring harness at the drivers side front of the bed. You have to get under there and dig it out. It does not have a connector installed.
06 RAM 3500,Dually,CTD,Auto(ATS Stage 1),QC,4X4,PacBrake,Spyntec Freespin Hubs,60 Gal Titan Tank,EFI Live, Line-X,Torklifts and SuperHitch,Fastguns
2013 Arctic Fox 990, 275 Watts Solar, 2 Grp 31 AGMs
US Navy 1964-1968, 2-Tour Vietnam Vet