I, too have this same problem with my wife's 2015 2LT RS. I replaced the bulbs today thinking that both of the lower-wattage filiments must have burned out. (the turn signals still worked) After installing new bulbs the result was the same. Then I looked closer at the wiring and noticed only two wires connected from the harness to each of the bulb sockets. So the sockets take 2-way bulbs but are only wired for the turn signals. I guess the lower amber lights on the bumper cover are the parking lights now along with the LED DRLs.
It appears that the older models used 2-way bulbs and the lower-wattage filaments were the parking lights and the higher-wattage filaments were the turn signals. Then when they went to the LED DRLs they kept the same bulb but eliminated one of the wires.
Oh well, at least I have two spares now.