There is no ABYC, NEC, or UL standard for shore power below 20A. By code, the 15A receptacles are for attended use only, for tools and similar. Does anyone know the reason there is no code for lower amps?
Marinco does sell 15A inlets for bass boats, but the assumption is that they are used for charging batteries while on the trailer.
And there is still the subject of ice melters with a #14 cord, which present pretty much the same hazard as a boat. They move continuously and are certainly not inspected frequently. Many are plugged into 30A-15A adapters. If they are plugged into 15A, you can bet they are not particularly weather proof.