They say that it is for ease and that it is hardship to keep it at 15°. I wish I was joking. In Toronto, those masajid that change to 12° in the summer even bring in these "fatawa" from people who are not even of the same maslak. For example, Ahmed Kutty is used as a fatwa source to justify something like this (as well as the 15° Fajr when it has been empirically proven that Fajr time begins at the 18° mark at the latest) - even by Deobandis when he is neither Deobandi nor Hanafi and holds a few strange beliefs in fiqh.