Originally posted by Des Perhaps Greg might weigh in here, but I notice that In posts in the last few years he reflects without great fondness on the 16-45 as lacking microcontrast and colour richness, even compared to the DA 12-24, let alone the DA 15 Limited and DA 16-85.
I was initially impressed with DA 16-45 because of it's corner to corner sharpness throughout it's range. But images from that lens just did not wear well with me over time. There was just something lacking in terms of clarity, contrast, color when compared to other Pentax lenses like the DA 12-24, DA 17-70, DA 16-85, FA 20-35, not to mention the star and limited lenses. I ended up replacing it with the FA 20-35.
A general adage regarding lenses is to get the best lens you can afford. Don't go cheap unless you absolutely have to. The best zoom lenses with wide angle coverage would be the DA* 11-18, the DA 16-85, the DA* 16-50, and the DA 20-40, followed by the DA 12-24 and DA 17-70.
I see the DA 15 as a specialist lens. It's harder to use than the zooms, and not just because it's a prime. It can be challenging to sharpness out of the lens away from the center, particularly at long distances, and my copy is never tack sharp at the very far edges or the corners. But if used right it's better at producing images with high impact than any of the zooms (with the possible exception of the DA* 11-18) listed above.
Here's a shot with the DA 15 taken at Patrick's Point SP: