They are in the back of the bed on both sides. Could it be for these?
http://www.mopar.com/part/82211058?s=362942&i=4309867&b=ram
Looks like they have two holes for Rivnuts.
They are not shown as compatible with a 2015 but mopar's site may not be updated yet.
jgillott - do you have any info on the LED bed lighting? That's something I am looking into.
TIA.
They could at least have a plastic snap in infill cover the holes.
after looking at the accessories for the 2015, another possibility is the extend-a-bed rack that looks as though it might use those holes to bolt the swivel rack into the sides, when it fold down onto the tailgate.