I'm running the APC 15/4W on the Mojo. It is about perfect for it. I used a 14/6 but found the same thing as you, the 15 is a much better "MoJo prop".
When the Engine was on the Cub, I also tried a 15/6 APC it worked fine for a Cub in scale flight but the takeoff rolls were a bit longer than ideal. the 14/6 was about perfect for general sport flying.