Thank you for your replies so far! I am not yet cured of my desire for the DA 14, though
Somehow I feel it would lend itself better to my photographic needs. I am not so keen on doing those sweeping, edge-to-edge sharp landscape pictures for which many people seem to use their ultra-wides most often. For those pictures I have no doubt that the DA 15 or DA 12-24 stopped down to f8 or so would probably be a better (or at least more convenient) choice.
I am more interested in making pictures that create tension between foreground and background, either by using contrasting subjects or by exaggerating the perspective. Or simply to show close objects (or people) in their surroundings. I feel that either the high minimum focus distance of the DA12-24 or the ugly (to my eyes) bokeh of the DA 15 might be problematic for these uses.
What stops me from buying right now is the fact that Pentax (according to their lens roadmap) are planning to release two new lenses this year that might affect my decision.
The first is the ~12-30 zoom that might be another interesting option if it is either smaller or closer-focusing than the existing DA 12-24.
The second is the ~20-40 "limited zoom", which sounds tempting. If I decided to get this later on, the DA 15
might be a better companion to it than it would be to my DA 17-70 now...