I have one of these but a much older model. I do brisket on it all the time and it is always good, if you like "Texas Style" brisket.
I am not sure what you are looking for here but I can tell you what I do.
First... It does not take 15 hours to smoke a brisket. I you arnt eating within 8 hrs of putting it on, you 'aint' using enough heat.
The old 'Low and Slow' is valid but within reason...
Also, after reading here, many like to mod everything (not that that is bad, but some of the things I see i wonder).
A little smoke leaking around a lid doesnt matter when its going out the chimney or lid when you open it anyway.
So here is what I do. ( not saying its right..Just works for me)
First find a nice Brisket that has some flex.. (look for a nice thick flat, that does not have too much fat, but you need some)
You need to be able to bend the brisket, meaning pick it up and make sure when you grab it on the ends you can almost make a U out of it. If you cant, keep looking.
I start the coals in the sidecar using a pretty good amount (4#s or so) and let them get about 75% white.
While the coals are getting happy,
(the next step can be done the night before and put in the fridge for best results but if you dont have time)
I take the Brisket and may or may not trim a little fat off it. ( it will break down and keep it moist anyway).
Season the brisket:
Course Blk Pepper
I coat it pretty good both sides (but do what you prefer here. Its big meat and needs big seasoning)
Once the coals are happy. throw some nice wood of your choosing. ( I like pecan or mesquite, but thats just me and I can get it in my back yard lol)
Put the Brisket (fat side up) on the grate and close the lid. Set the damper about 1/2 open close the sidecar lid and let it smoke like hell.
Now, here is wear people are going to come out of the woodwork. (im ready for the attack lol)
Dont worry if you are at 300-325 degrees on the gauge for now, you need to get things rolling and extra heat is how you do it.
just make sure you put enough wood on it to get it really smoking heavy..
You want to eventually get the heat to around 250, and it will get there just fine, Just make sure you add coal and wood as need.
Once you have heavy smoke on the meat for a couple of hours , that is all you are going to get flavor wise anyway. So after that you are just cooking.
Go drink a few beers and after a hour or so open the lid and roll it over. (repeat / repeat / repeat)
Dont ever stab the meat (ie with a fork) always roll it over.
(scud launch coming lol)
After about 5 or 6 hours when it is a nice dark brown juices are flowing clear.
wrap that puppy up with some wide heavy duty foil. and go drink a beer, hard part is over.
make sure you have some good heat 250-300 at this point so that it keep cooking.
(the foil just keeps the juices in and keeps it moist)
couple of hours and you should be salivating.
Couple of Sidenotes:
you can mop the brisket during the process as well, and I do this more times than not, but this is a fail proof method to have some delicious tender meat...
Here is the one I did last weekend..