I can set the max charge voltage on my Bogart solar controller. I think I dropped it to 15V.
I don’t understand the comment about 15.5 not reaching the electrical components. The controller output connects directly to the battery, so it’s the same voltage to the battery and the camper electrical components. I guess you could put a regulator between the battery and the “main out” to the camper, but I don’t think that is how they are typically wired.
I think the only downside of dropping the voltage is slower charging at low temperature (assuming you have temperature compensation).