The 15mm stays on the E-PL1 and I carry it with the E-M5 plus 17mm or 20mm mounted. Both of them fit in the center console of the Prius with room to spare. And that's a good thing, actually. With Pens I can keep them hidden in the car at all time and not worry nearly as much as I did in the past with the larger DSLRs. In fact the E-PL1 with the 15mm is very pocketable, or at least with the kinds of pockets I have on my pants. And I'm not talking cargo pants.
If you're coming here to look for IQ then you should stop reading and head on somewhere else. The 15mm only has two focus settings, infinity and close focus. At infinity and f/8 it has a a rather profound depth of field. The close focusing position is a bit of a moot point for me.
While I was out and about with the 15mm I used the various E-PL1 art filters; poster color, diorama, and black and white. I could have probably used the vivid color selection and still gotten saturated colors in the photos, but the art filters pushed the photos over the top and added to the photos.
I think what I like about the 15mm with any of the inexpensive Pen bodies is that the whole combination is stripped down to its essential elements; a fixed focal length lens with fixed aperture, shutter release and sensor. And when I get home I hook the camera up directly to the Mac, run Viewer 2 to scale the photos and pull them off the card and then do with them as I will. It's a simple and enjoyable workflow, and a great way to practice shutter therapy.