With 15W tube amp, which speakers to use?

Triangle Titus are very transparent and natural sounding, go for a pittance these days and work very well with most any wattage. They are exceptional at low volumes but show no signs of stress when run at higher SPLs. They are small and front ported and can be located almost anywhere with very good to excellent results.

The Devore Super 8s works well with 15watts of amplification based on what i gather frm reviews and end users

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.