"Is there a reason why this may be, and are there any lower sensitivity 15" drivers that I could think about. Power is not an issue as I have a 1000Wpc Ice amp available."
There may well be reasons, but if so, they’re above my pay grade. I’m no driver designer or TS parameter expert. But, I think that it’s not so much that there might be exceptions, so much as there might be ’near-exceptions’ to some sort of iron law for it that I’ve never been able to work out. Part of that problem is that traditionally woofers are hardly ever designed for specific applications from the ground up, instead they’re usually ’crosspollinated’ and shoehorned into more or less filling a need. Many, many woofer designs out there are "dual" or "multi" purpose, convenient for the manufacturer maybe, but a compromise for the user no matter which way with them you go.
That’s really what I happen to like about Acoustic Elegance. John up there in Michigan never makes a woofer until he has gone back to the drawing board and has fully and independently designed and manufactured, all in-house, just one, single, definitive model (from any, one maker, that should be all you need) for each and every possible woofer category (infinite-baffle, bass-reflex, bandpass, sealed, etc, etc)...no need screw around with anything dual-purpose ever again. That allows you to start with the app alone and then buy someone’s deliberately best-conceived design for that app. From there, you basically just choose the woofer size, and how many of them, you need. What you get is something designed for your, particular app that was never compromised from the start.
But, don’t let anyone kid you, bass response in the room is really one of the very hardest things to get right in all of audio, even when going ’by the book’. And depending on how ambitious or not you want to be with it all will certainly dictate what you might want to try. But, IME, I find that the ’just right’ level of bass performance is a very difficult thing to try ’sneak up on’ and hit on without any overspending at all. For my money, it’s much more successful to get a better woofer and ask it to do something Less than it was designed to do than to ask of the ’just-right’ woofer to do something More than it was designed to do.
In fact, if it were me, I’d be looking at using only one, good driver type (per side) below your 200 Hz xover point. That way you can eliminate the xover to the sub altogether. That’s very important to the overall character of the bass response in the room. The fewer xover points the better, with 3-way systems sounding nearly Always the best, overall. Crossover effects are actually quite audible and even the very best and most expensive of them will degrade the sound to some extent, and if not so much in frequency, then in terms of coherency and dynamics. I think those sorts of advantages can often end up being the first casualties when we get too caught up in chasing the lines on a graph.
Of course, all this is just my 2 cents and it’s mostly so much audio philosophy, but it’s maybe the kind of thing that if my present-day self could go back in time and give audio advice to my 30-year younger self, it would likely include something like that.