Fold n' stuff is simpler and faster than the traditional loading method of a loose cut or rub IMO. However, if you only have 15-20 minutes to smoke, then I'm not sure a flake is your best option. It will require some prep time to determine the amount you would need to cut from the flake for the amount of time you have to smoke. There's no way to smoke a whole flake in that amount of time. I've had one Mac Baren Navy Flake last over for 2 hours before.
If you don't mind not finishing the tobacco, then flake is good for two other reasons: It's does well outside and I've heard that it can have a DGT - Delayed Gratification Technique.
"If you are unfamiliar with the term Delayed Gratification Technique, or DGT, it is simply this: light your pipe and smoke part of it, but leave at least half a bowl unsmoked. Then put it down, allow it to go out, and re-light it again some time later."