I have a Hama pinch cap that fits, but I don't think that I will be using it. The threads on the filter ring of the DA15 are rather shallow so the snap-on cap is not as secure as with some other lenses. I would hate to have the cap pop off and scratch the coating on the front element. I don't think that I would trust any snap cap with this lens.
I also have a generic metal screw cap that fits. It would be a better replacement (since it can't come off accidentally), but it is much harder to remove than the original cap. The dedicated Pentax cap is a brilliant design. The way the knurled knob extends out past the lens makes it very easy to use in comparison with other screw-on caps. The dedicated Pentax cap can be purchased for about $30. While I haven't lost mine yet I think that I will order a spare.
By the way, I kind of screwed up in that I waited so long to order the DA15. If had known how great the overall image quality is and how much fun it is to use I would have ordered it sooner. If anyone reading this is contemplating the purchase of this lens, do yourself a favor and just buy it.
Dan