I'm going to put one on my 2500 6.4L soon and I'll let ya know.
Several things I have found out:
1. No tuning available for the 2015's yet due to encrypted code on the PCM. They are working on it but don't hold your breath. It could be a while.
2. Diablosport tuner canned tunes won't generate massive gains, however, the improvement in HP and torque at lower RPM's really makes the truck feel more responsive.
3. Custom tunes are the way to go, IMHO. I did a custom tune on my 5.7L 2007 MegaCab and on my 6.1L 2006 300C SRT8 and the changes are amazing.
With the addition of a cold air intake and freer flowing exhaust you'll maximize your performance and efficiency by adding a tuner.
Just my .02 on the subject.