Dynaudio BM15As in smallish rooms

[love_tempo]

I'm about to replace my Dynaudio BM5 passives and amplifier for active models with more bass extension.

I was about to get Dynaudio BM6As new for about £900 but noticed that there are some second hand BM15As locally for a little less than that. I can't seem to source second hand BM6As. Could this mean 6As are that bit more desirable/practical?

I wonder which would be a better buy for me bearing in mind that my current room is small (17 ft. x 15 ft. x 12 ft.). They would likely be my last speaker purchase for a good many years and will be my main home listening speakers too. I listen to a wide range of music but produce fairly bass heavy electronic music and also record female voice, guitars and violins.