75" Samsung Q80R QLED, Denon AVR3300, Revel F36, C25, W263, FV15HP x 2, ATV4K, Sony Blu Ray, Harmony
3 dB will likely make a nice difference in my opinion, especially considering the large space you are dealing with. At higher output levels, each dB or two of SPL in bass becomes quite noticeable. More so than a dB or 2 or 3 at low volumes.The "less than helpful" was in reference to the questions I asked about the differences between the two 15" models that went unanswered - it had nothing to do with his suggestion about needing more subs to pressurize the space, which I found insightful as I hadn't heard that before. But I didn't specify that in my post, so apologies if I misled. Have gotten good feedback from some of the posters here.
oh....and you know what they say about people who make assumptions.
For example, if your subs hit their limits at say, 110 dB on an LFE scene, and bigger subs will play the scene at 113 dB, it would be a quite noticeable difference and feel a lot more powerful.
Another way to look at it is going from 2 FVX15's to 3 FVX15's would add, best case scenario, 3 dB for an additional $1100 cost. Dual FV15's give you this added SPL for a smaller cost difference.