The 15x12 is an awesome prop, I have yet to meet anyone with one who isn't happy. You loose a little speed off the top end, but that's the only negative I have found. It's fun to keep loading the boat up and not having to worry about there being too much weight. We had over 4k in my X-30 this summer with 8+ people (and the X-30 weighs 4700lbs dry) so it was over 10k total weight and we got on plane no problem. Wake was bananas with that much weight too.
2013 X-30, 6.0L with 2500lbs of ballast and 500 lbs of lead.