+1 for hiking with the DA15mm Ltd. I have the non-HD and it is great on the K-3. I also used it with my older K-7, a backup body. The results are superb at low ISO. All in all the DA15mm Ltd is highly recommended, for landscape, as well as urban shooting.
I posted there a few shots with the Da15mm a few years back:
Primes in Paris - PentaxForums.com
While I use zoom lenses, I tend to prefer primes for the IQ and light weight. The DA15mm is also a nibble: it is very easy to put in and out of the bag a dSLR body with the DA15mm. For hiking, I sometimes carry another prime in my pockets, often the FA77mm Ltd as a short tele. Other Pentaxians talk positively of the DA70mm Ltd also, another pancake lens.
My 5 cents.