As you can see, there are different ways and differing opinions. I've done seven 8+lb butts on one of my 22.5" WSMs and I rotated about half way to try and have them all finish reasonably close. In my experience, without rotating, the ones on the bottom rack can take several hours longer. Since you have 15 hours, this might not be a big deal. This can work, but may want to rotate the meat and may have to reload the smoker after ~ 10 hours (again...just my experience).
The other approach mentioned most is doing 4 on each of the 18.5" WSMs. I would tend to lean towards this approach as my 18.5" was more efficient and you most likely won't have to reload during the cook.
Either way (or using just the top rack of all 3), have fun and take some pictures!
The other approach mentioned most is doing 4 on each of the 18.5" WSMs. I would tend to lean towards this approach as my 18.5" was more efficient and you most likely won't have to reload during the cook.
Either way (or using just the top rack of all 3), have fun and take some pictures!