I work with the BM15a's in a room the size of a bedroom and have worked with the BM6a?s in a similarly sized edit suite. IMO the headroom offered by the 15a?s is a significant advantage over the 6a?s. I find no problem with mixing at conservative levels. The work I do (dance music and sound design) pushes the upper end of what the 6a?s were designed for, especially in the low end, but the 15a?s handle it all with ease without excessive volume. I don't believe you'd regret buying the 15a's now. Best, -J.