Originally posted by Wasp Ultra wide lenses such as 15mm and 20mm were expensive back when they were sold new. That means that relatively few were sold and produced, making them rare. The bottom line is that it's a seller's market as far as UWA goes.
Pentax once ran an ad campaign on how few 15mm lenses they sold.
I have the A version of that lens. When I ordered it, I was told it would be a bit of a wait, as it had to be assembled for me in Japan. I joked that if they were doing a build to order would it be possible to put a little plaque on it saying "Custom built for Wheatfield"? That, unfortunately, wasn't done. I think it would have been really cool.
Anyway, even if it doesn't say so, my A15/3.5 was custom built for Wheatfield.
When I bought it, the DA 15mm lens hadn't been marketed yet, and so I was using it as a semi wide angle on whatever APS-C camera I was using at the time.
I'm quite fond of the thing, especially now that I can use it on a full frame camera. It's not the sharpest tool in the shed, and it vignettes quite badly, but it's such a cool looking lens.