Not long ago, I referenced taking "two of the world's best wide angle lenses" with me to Ricketts Glen State Park. The sample picture I shared was taken with the Canon TS-E 24mm f/3.5L II Tilt-Shift Lens, but I did not address the other lens I was referring to.
As you may have now deduced, the Zeiss ZE 15 was indeed that lens. This awesome lens is now my primary ultra-wide angle lens when AF or a range of focal lengths is not required.
Check out the Zeiss 15mm f/2.8 Distagon T* ZE Lens Review.