Every brisket I cook is in the 14-15 lb range. Every single time it takes 7 hours.
I cook at 250, foil when it hits 170, pull when probe tender which is usually 200-205.
Some say the Backwoods (and Backwoods type cookers) cook faster. That may be... but I have never had a brisket take 10 hours.
Best of luck to you.