With 15W tube amp, which speakers to use?

I have not heard any of these so I can not speak to their attriubutes. I was considering going in your direction(15wpc SET)and was told to try Coincident, Triangle, Omega, Klipsch,Cain & Cain. As you know speaker selection is very difficult with this low of wattage. Good Luck

Cain & Cain is an interesting choice. Never heard them, but I love the way they look and the single driver design. Also I understand they are very efficient and hence a good match on paper.

Single driver speakers are always efficient due to the absence of power absorbing crossover network. The drawback with most of them is limited bandwidth. Various manufacturers have found ways to stretch the laws of physics to compensate for this to varying degrees. Size and budget will be more limiting for you than number and variety of options. I like Zu.

I use Zu Druids with a 2x15W amp (KT88s), they will fill even a large room with ease. Next to the usual suspects from Klipsch also watch out for WLM Divas with their more refined character.

DCM TFE-200. I heard these demo'd at HE2007 in NYC, run off the Jolida integrated with 15 watts/channel. Truely impressive, and this was a larger meeting room, not one of the tiny guest rooms. The sound was smooth, dynamic, extended, with a very large soundstage. They're cheap, too. www.dcmspeakers.com