Zeiss is sharper, as expected. And for the person asking whether it would really be worth the difference since the 135L is so great, I'll tell you this: I loved my 100L Macro, but I really, really, really love my ZE100 (even though it was 2x the price and doesn't have AF or IS).
I'd love to replace my 14LII with the ZE 15, but $3k for 1 UWA prime just seems silly to me. Might get the ZE 135 eventually, but I'm happy with my 135L and dont use the focal length too much anyways.