It looks like the Zeiss is better in the mid frame and edges. But both lens are very sharp. For the way I would use such a lens, I think the sharpness in the edges and midframe would Zeiss the edge here.

For me, whether I choose one or the other, the deciding factor could very well be filters. The 14m uses drop in filters and has a front lens that bulbs out. The 15mm appears that it can handle a screwed front filter.

I had a 14mm for about a week, and sent it back and got a 16-35mm II instead. I wouldn't mind having a super wide lens in my kit. I still go back and look at some of my pictures I took with it, and they are great. Coupled with DXO it would be a great lens to have for the current assignment.

I would be happy with either lens attached to my camera, no matter what it looks like.