Steve, if you're looking for 3D performance with hovering and other prop hanging stunts being a priority then you are best to stay with props in the 3 to 6 inch pitch range and experiment with options until you find the one that works best for you and your model. But I'm pretty sure you won't find a 15x3 and even a 15x4 is going to be scarce. For example I see that APC only makes a 15x6 as the finest in that diameter but they do have a 14x4W that is spec'ed for Funfly.

Paul, nice sound track. You can definetly hear the difference.