Ram gives the 2500 truck a 6000 or a 6200 or a 6500 rawr depending on cab and other selections which will carry 98-100 percent of the payload. Your trucks RAWR is on the door post cert placard.
My '03 2500 Dodge/Cummins 2wd QC NV5600 tranny has a 6000 rawr. My trucks rear axle weighs 2840 lbs leaving around 3160 lb for a load in the bed. I wouldn't assume everyones 2500 Dodge/Ram weighs the same as mine. I also keep scale tickets (front and rear axle) in all of my trucks....that way I know if I'm exceeding a axle/tire/rear suspension or wheel capacity.
If your '15 is like my '03 it has no aux upper overload spring pack. Mine squats in the rear with 1600 lbs in the bed over the axle.
I tried the Timbrens but they were only 2 3/4" long with 1" gap for a stock ride on my 2500 2wd truck. This created a short compression and a violent rebound of the rear suspension. Terrible ride.
I went with Supersprings.
However if you feel a need for air bags for leveling the truck or carrying more load then thats what I would do. Air bags with controls in the cab would be a good upgrade.