As the cost and weight of a 3015LF-based cab climbs, it starts having to compete with a 2 x 3012LF cab. In my opinion the sweet spot for the 3015LF would be a two-way, and I have not yet found an economical way to offer a worthy alternative to the fEarful and its cousins.
That makes some good sense. It's tough to get sufficient output out of a 2-way with a 15 without making the crossover or the HF section inordinately expensive.
I imagine it crosses over into Bill's territory a bit, but here're a couple thoughts;
-horn loading a smaller midrange driver (like a Faital 5, or a pair of those B&C 3" mids) - I don't know if it's got the right specs for it, but its on-axis performance is solid, so a boost in efficiency from horn loading might make it enough to keep up with the 3015LF (and further its higher top end extension than the 6nd410/6nm410 might help some).
-partial horn-loading the 3015LF to improve its radiation pattern up to the point where it could be crossed to a horn at a frequency that is suitable for a less costly crossover. I believe Bill's O15 does this but then uses a mid horn crossed in the 1200hz range. Might be you could make some different choices there.
Personally I think you'd make more money moving to a 2x10 than a 15, though, given current stage of perceptions in the industry.