RE: Faster flight using different prop, Question?
Marshall,
I agree with Matt but i'm not sure if APC makes a 15x12 e-prop. [link=http://www.hobby-lobby.com/elecprop.htm]Hobby Lobby[/link] has a 15x10 prop that may effectively give you more speed. If the current is reduced on your Lithium pack, the voltage will be higher which will produce higher RPMs.
It might be worth a try if you don't easily find a 15x12 prop.