I recently replaced a Puritan PSM156 with a P15. I agree with @jeffbij that it is an improvement, relaxed and smoother, is a good description. My goal was to have “Sunday night sound” all of the time, and I am pretty close to that with the P15. I should caution though, it was not a religious experience or a night and day difference in my case, but definitely an improvement and worth the investment in my system.
ASR reviews can be useful in certain cases, but they are only one data point. While their measurements might be accurate, I don’t think their conclusion is valid for the Powerplants.