Yeah, The NC ability of QC15 is quite good, but Ziks is much smarter,.
The Zik's NC is likely the best next to the QC15s. But I've had them on loan for a few days and found the wireless features buggy.
You should try the QC20i...wow! I never thought NC would get this good and they sound pretty darn good (a good step up from the QC15s).