I don't think I've ever seen anything that's coupled shorter than 28mm. Everything else seems to come with an auxiliary finder and scale focusing...although the depth of field on short lenses is so huge that this probably isn't a problem (especially at the 15mm end).

I've read lots of good stuff on the Voigtlander 15mm lens. If you're going to dedicate one camera to a very short lens, then the old Bessa L is $69 at CameraQuest. It has a meter but no viewfinder or rangefinder...but with a 15mm lens and the auxiliary viewfinder attached I don't think you'll need either of those. I've been toying around with the idea of picking up this set just for "special effects" use...under $420 for a set that'll shoot 15mm rectilinear. At f11 you'll get pretty much everything from about two feet to infinity in focus. (Sets like this show up on eBay from time to time, but I haven't tracked how much they sell for there. It might be worth keeping your eyes open there.)