I had the 14mm and liked it quite a bit but when I compared it to my 16-50, I found there was a warm colour-cast to the 14mm and it didn't quite match the sharpness of the 16-50. I also found that with the 14mm, I couldn't use my landscape filters on a cokin P holder without vignetting. With the 15mm, it maintains the neutral colours of the DA*, is much smaller than the 14mm and you only loose a stop. As for filters, my Singh-rays are back in action
. I'd therefore choose the 15mm without any hesitation.