I have two Duo-Therm 15k heat pump penguin AC units on our camper. One is down to 10 deg differential temperature suggesting it is loosing Freon. Compressor currents are nominal or maybe a little low....
I will say this: IF it is loosing freon the odds are you have a tiny leak.. A good A/C technician may be able to find and correct it for a couple hundred dollars... HOWEVER.
I had a major leak, and the location did not make repair easy.. (I have A/C only not heat pump by the way)
The original was a 13,500 BTU, it pulled 13.5 amps running. The replacement 15,000 and pulls the exact same 13.5 amps running.