This is purely related to IDPA in Central Texas, so your mileage may vary.
I have found the change to 15 rounds to be a non event. Stages still typically are large enough to require a reload. Its frankly a pain as my P320 mags only show 10 and 17 rounds, which means I effectively have to get down to 10 rounds to know how many are in a mag after each stage, and at 12 rounds really requires a mag loader.