As Old'sCool suggests, your probably good. But if you want to keep splitting hairs, definitely trade the 19 for 15p.
If the diameter is a little greater on the 15 it might not be as big rpm increase as you think, and even less increase if you were not carrying your max projected load on your test runs.
I was amazed at the difference between a 17 and a 15p black max/diamond.
The Nemisis appears to be a 4 blade clone of the black diamond blade shape. What strikes me is QS's claim of a 25% improvement hole-shot improvement over the Black Diamond. That sounds scary.
I must try this. Where are you finding this prop for $90?