Small yet Amazing
+ Small size
+ Optically excellent
+ Built-in hood
- Screw-in cap
To me, above everything else, the size of the DA15ltd makes it a winner to me. I do a lot of street and travel photography with this lens. Whereas my previous wide-angle (DA12-24) was very, very big and intimidating, the DA15 is so small it doesn't make people self-conscious. This is an often overlooked but to me very important aspect of this lens. The small size also means I can carry my entire kit in a very small bag.
Optically this lens has a lot going for it. Contrast, colour rendition and sharpness are all stellar. As the other review notes, corner softness has never been a real world annoyance. The situation when you end up using this lens wide-open don't require corner sharpness, and the situations where you want corner sharpness do not require a big aperture.
The Build Quality is downright excellent. The screw-in cap is perhaps not as convenient as snap-on types, but the excellent built-in hood more than makes up for that.
This lens is my most used lens by a big margin. All in all I think the DA15ltd is the single biggest reason why I prefer Pentax over any other brand. No other DSLR maker has, at the moment of writing, a lens this wide yet this small.