The main reason I feel that you want dual double 12" or dual triples is the settling time of the drivers. More drivers mean less excursion, less excursion, means faster settling, which means a clean effortless sound. Doesn't mean they have to play louder... but they can
Especially if you're going to live next to someone (share walls) I would suggest OB bass even more. They won't pressurize the room as much or "boom" the room which will cause additional vibrations that will resonate throughout the house/condo/apt into your neighbors ears and feet
Just because something is bigger doesn't mean it will vibrate the house more. If anything it will have the opposite; just be able to play much louder and boom the house more at that point. But compared at same SPL levels it will be at least the same amount of boom if not less with more drivers/bigger enclosures. You can also help your cause with experimenting with different way footers/isolation platforms. I spent $100 on some SVS footers, which are basically an innertube per foot, and they drastically reduced the vibrations throughout the room, even on a sealed 15".
But if you go with open baffle anywhere, or expect you will in the future... Do it right off the bat with the subs as well. I wish I did.... no wait, I mean.. do you want to buy a Rythmik F15HP??