Both versions are fine lenses and show remarkable low barrel distortion for subjects in the middle to distant range. Up close their CRC creates significant barrel distortion, just like the 35/1.4. Central sharpness is excellent, although the f/5.6 struggles more on a digital camera due to its uneven colour rendition across the frame and its corners can be on the slightly soft side. The f/3.5 is largely devoid of these problems. Their CA tends to be of the lateral kind and thus easy to remove.
They are very prone to flare when bright light is just outside the frame, and the f/5.6 being extremely susceptible to flare will do so on the slightest provocation, even the presence of ordinary sky light is enough.
The f/5.6 has built-in filters on a turret and the f/3.5 uses the same small rear filters as the larger 13/5.6 and the (in comparison) tiny 16/2.8 Fish.
The 15/5.6 was the first occasion I encountered of a Nikkor with severe decentering issues, by the way. I finally had to have my sample replaced by Nikon, as the factory did not manage to get it in proper working order despite the lens being returned twice to Japan. The "new" sample has served me well since 1973, though.
