As for 15W lamps for darkroom lights: why not use lamps for fridges ?
I have never seen anything other than the traditional incandescents in them.
If your darkroom lamp has a big socket replace it with a small one, it is not that dificult.
My biggest worry right now would be the lamps for the enlarger heads if they do use the "wrong" type of lamp.
Finding a good replacement for them, esp the condensor type could get hard, in a difusor box you would have more options.