I have and (occasionally) use its antecedent, the 15mm f/3.5 Super-Elmar-R, purchased slightly used from a local camera store owner about 15 years ago. As one might suspect, this is glass not built to a price point and its resolution is quite amazing. The only difficulties I have with this lens are two: I can't seem to keep my shoe tips out of the picture frame when hand-holding (!) and its closest relative, the 19mm Elmarit, is an even more amazing, sharper ultra wide!
The 15mm f/3.5 Super-Elmar-R is the same as the C/Y 15mm Distagon and is made by Carl Zeiss Oberkochen for Leica-R. The 15mm f/2.8 ASPH is made by Schneider-Kreunach for the Leica-R camera. Both excellent lenses showing their best optical quality at f/stop 5,6! So, it is really not required to look out for the very expensive and rare lens with f/stop 2.8. Cheers
Hi I had the F3.5 and used it on a Canon 1ds Mark III I was somewhat disappointed finding that other wides I tried had about the same image quality for less cost. Having said that I had been tolled that the Leica f2.8 was much better.