I would say that banner is no more than 16' x 32' (512 sq ft and I am being generous on the size of it) - so no more than 15 minutes to actually print out on the superwide inklet printer I mentioned above which can do 2240 sq ft in one hour.
inklet = inkjet
Your calculation would be accurate if the banner contained a high percentage (80% or more) of white space. This banner is less than 20% white space and high resolution. Compare the time an inkjet printer takes to print a page of text (even multi color) and a full page color photo. The time differential is significant a factor of 6 or higher. This banner didn't print in 15 minutes. More likely 1.5 hours or more.