I have the DA14 as well, I really like it, something that hasn't been mentioned yet that's also very nice is that the focusing ring doesn't turn when AFing.
I use it wide open or stopped down just a little (f3.5 or so) , especially in close focusing situations where you can actually get some bokeh then, see this shot:
The f2.8 aperture also helps more precise manual focusing with a brighter viewfinder and shallower dof in the viewfinder.
That being said it IS way bigger and heavier than the 15mm, especially with the hood it is huge, so I end up storing the hood separately in my backpack most of the time. Also it is difficult to use the built-in flash as a fill flash with the lens because the barrel blocks the flash a little. (I have found a remedy for this, take your photo upside down
If I were to choose again I would probably choose the 15 for its size.