There must be some "intelligence" between the truck alternator and the trailer.
Those readings sound fine to me. Indicates that the electronics has determined that the trailer battery is getting full and is cutting back the voltage to it.
I've noticed that my truck voltage stays up around 15 much of the time too but haven't paid real close attention. I would think it too should drop back to about 14 if that battery comes up near full.
This post just reminded me that I need to check the water in the truck battery before going out again.
