Your P3 feels that a wattage level above 14.6 is not recommended for the setup you are using. If anything a P3 is all about safety. So my question is what is the vape like for you a just below the 14.6 level? Just because you have 20 watts available, doesn't mean you need to use them all to produce a very satisfying vape. From the Users manual for a P3:
Reduce Volts / Watts or Replace Atomizer
This error can occur if the voltage or wattage is set too high and P3 cannot safely power the atomizer with your current settings. This can also happen if you
have the voltage or wattage set too high along with the boost mode set too high. Try lowering your settings. Most of the time, if you have these power
settings too high, you will be burning the juice and it won’t taste very good or you risk burning out your atomizer.
I too have a P3 and exclusively use Kayfun (authentic only) on it. Many of my builds are 1.3 - 1.5 ohm. For a great vape, I have not yet needed to vape higher than 10 watts.