As Grumpy said there should be a tag stuck to the axle. If you have a standard edition it might be a little difficult to crawl under it to check. Our 2015 195RB Baja edition has a Dexter D35 3500lb axle and I suspect yours will be the same. You can download a copy of the manual from Dexter's website once you confirm your size.
TT: 2015 Jay Flight SLX 195RB Baja Edition
TV: 2014 RAM 1500 Big Horn CC, 5.7L Hemi, 8-spd, 3.21LSD, Factory Air Ride/Tow Pkg, Andersen WD/SC