re: Question about cooking large quantities of pork butts

You absolutely do not need to cook them longer. Your cook time will not differ whether you have 1 butt or 16 butts (as long as there is space in between the butts and they aren’t piled on top of each other).

And as long as your smoker can handle the amount of meat and you don’t have issues keeping your temperature up (which I wouldn’t think you would).