The guys I know who broke 160 have done it in a sixth order.
with 55,000W and 1600 square inches of cone area. The vast majority of the youtube bandpass builds (and really everything besides the top secret stuff that DB Drag leaderboard top 5 guys use) would do the same numbers in sealed box with the power and cone area they run.
Even Terry Brock doesn't use any of that nonsense in trunk builds that BTFO everybody else in trunk classes by 5-6dB.
I've looked at a lot of different 15" subs and have yet to see one call for 7 cubes ported, have you?
Yes, some of the Atomic SPL lineup, in fact there was a guy on this forum within the past year talking about them, and Shocker Mike always told me sigs gain up to 8 or 10 cube then you do better with 18s. DD9515 do very well in >5 cube boxes as do Fi SP4. I'd imagine several more similar design concept 15" subs will also gain efficiency up to about 8-10 cube per.
I've done a lot more testing with 12s and with that motor a 12 will be louder than a 15 right up to almost 5 cube so I have no reason to doubt Mike's testing with larger cones. Anyway, I don't think anybody commenting has ever used the subs OP named so why comment if you haven't used them, haven't modeled them, and haven't tested any 15" sub in a lot of airspace?
Kicker square 15's are cone area of a round 18 and will want a lot more space than Kicker recommends. I've played with a couple Solo X 18s and seen a good bit of Kicker in the area besides and guys that do good numbers with them use boxes nearly double kicker recommended.
Anyway, the reason manufacturers claim less space is because they know the consumers are mostly ignorant goons that only care about bragging rights as to how much cone area they have and how big of a number is printed on the heatsink of their amp (or the more savvy consumers how much Steve Meade dynos out of that amp). The company that promises the most cone area in the least volume will sell more and larger woofers. DC made a name for themselves like this and Kicker had a great run with the original round solo-baric with the same marketing. In both of their defense both do perform well in smaller boxes, but also both will gain with more volume behind them.
Why didn't you call Pop out?
Because he has significantly more experience and just asked the question. And a valid question since that is on the high side and can get into mechanical trouble. You'll notice OP tried less airspace, wasn't happy and was happy with them in 6 cube each. All things being equal he will gain output and efficiency going up to 7 cube provided he isn't at the mechanical limits of his subs.
Build more boxes, test every variable you can think of, buy a meter and take measurements, lurk more.