Coldsteel,
From just a quick look at the specs for Parsun vs Yamaha on web site, they seem to be a little different motors(displacement,fuel tank configuration,options,etc). I'm not sure how accurate the Parsun data was that I was looking at as it seemed to show the same displacement for the 15 hp as the 9.9 hp. Also there are lots of models to compare so it probably will take a lot more research (best would be to talk to an experienced outboard mechanic). I am thinking about repowering too and the Yamaha 9.9 high thrust model looks like a good choice but it is pretty expensive. Anybody with input on the high thrust model?