I'm in the process of finishing the wiring to mine. I went with 50A service even though I might not ever need it. Several reasons:
1. I can check out the function of the whole RV at once before I hit the road to make sure everything is working. I can turn the water heater and refrigerator on electric and check out ACs and other things while the other stuff has time to do its thing. I also have enough extra power to run tools like a compressor if needed for repairs.
2. If I ever needed to stay in the RV in an emergency or had guests arrive in an RV, I'm covered whether it's January or July.
3. The trench for the wiring costs the same for 50A as it would for 15A, but if I ever had to go back and upgrade I'd have to pay again so I might as well cover it this time.