Well, it actually wasn't up to me, but I am VERY happy I got what I got.
I do think the 10x12 is an awesome coil, too. Many members in the club I belong to(Metal Detecting Association of the Carolinas-MDAC) have been using this coil and have been getting great results. I feel that with the 15x12, you are definitely maximizing your detector's ability(MXT in my case) to get down to the relics that haven't been hit yet, the ability to separate between 2 targets, and spot-on pinpointing for a large coil!
Let me know if you have any other questions! I'd be happy to answer them for you.
The question about the weight differences, I'm going to see if I can get that information available. I've had many people ask that question and the best I could answer is that it weighs more than the super 12, but I don't know by how much...