Reading through the order guide again. It shows rear 3 seats in the long 15pax configuration are not removable. Does this mean that it’s more difficult to remove them or they really can never be removed?
The 5th row (and passenger side 4th) exterior seats previously had a large torx head bolt holding them down, rather than the spring-loaded release handle in all the rest of the rows. Here's a pic of the rails, and you can see the difference in the seats on the passenger side, and the one mount next to the rear A/C. At least in 2020 the 3rd row single seat had changed to the spring-loaded release.
So yes you can remove the seats though it requires a little more effort. The other downside of that is the mount sits above the floor slightly, rather than being flush/below the floor level:
I had the floor up awhile ago on a failed project and tried to make it productive by taking some general measurements of seat rail and bolt locations for my 15 passenger 2018 148". I realized I never shared this, in case it helps somebody. Not sure how consistent spare tire mechanism or other...
Oh ya, and there is a good video on Youtube I saw before I even ordered my Passenger van that I still have bookmarked. I wanted a Passenger van with the least number of seats so did a lot of Googling at the time. I think this will be bookmarked to his explanation on how to remove the "fixed" seats ... more involved than that single torx bolt.
If if doesn't start at the right point, fast forward to 23:45: