How big of Turkey can I smoke?
A few minutes on the Traeger site reveals that all their recipes call for Turkeys that are 15 pounds and under, so I'd go with that.
Your problem may not be with width or length but with height to top of smoker cover. Depends on where the grate is situated.
Very few birds are bigger than 15 by 20. We get 30-pounders that are roughly that size, but depends on the physique of the particular bird.
I am not sure 15 will fit. I may have to do a quick measurement and hit the grocery store to compare.
There are many different sizes of Traegers so when I looked through the site it was unclear to me as to which size MINE would fit regardless of what is stated in the recipes.
My instruction book says nothing about max size of bird.