My only problem with a four 15" WO is that I don't have a fork lift anymore. I used to have nothing but fun stacking my 350 lb folded horns up. Those were younger and more energetic days.
Last week I set my 2 iso-loaded 10" WOs up in a club for some friends and everyone (including me, a fairly old, salty crusted, PA tech type who has seen everything, I thought) was very impressed. It was the first time I actually heard them with live music. They had an old Peavey 400W/channel amp and the WOs really sound powerful sitting on the floor in a small club (about 350 seats).
This afternoon I'll be setting them up in a place more than 4 times larger. Since it is Jack's favorite "sounding" gig spot, I'm calling tonight the WO/Jack Acid Test. They will still have way more BASS than ever before, so I expect everything to be "all good". So far, I am very pleased with the 10" WO.
With 15"ers the size will be a concern. I have read about someone planning a 48" WO project using 15" drivers, but never a follow-up thread. I know scaling all 3 dimensions for a 15" comes out about 54" X 54" X 20", but I don't know if it's necessary to scale in 3 dimensions for a great sounding box. My plans, in the spring, are to build a set of Imperials and a 48" X 48" X 18" WO using a surplus of JBL E140s I have laying around from the old days. As yet, I've not done it.
My point is that you are sort of on your own, but with an audience of many "Monday morning armchair quarterbacks" ready to tell you what to do. I hope it all happens soon so we can start some history here.
Some old threads:
https://www.decware.com/cgi-bin/yabb/YaBB.cgi?board=Wicked;action=display;num=10...https://www.decware.com/cgi-bin/yabb/YaBB.cgi?board=Wicked;action=display;num=10...Looks like BigAir is the only one to actually build a 15" WO and post pics, but notice the radically angled baffle board.