For what it is worth, I've had very sharp results so far with the CV 15mm on a NEX-7. For this particular field of view, this lens produces results as good as any other lens and camera combo that I had tried. Fine detail is rendered with remarkable clarity across the image. Others have observed a marked drop in sharpness as the edges are approached. My particular copy seems to be much better than those other lenses tested. The results from this one easily make the extra processing with Cornerfix (to remove the magenta cast and vignetting) worthwhile. My copy happens to be one of the older Leica-thread (M39) mount versions. Adapters are readily available. If you go this route, may you find an excellent copy.
Regards, Rick