If it's over an hour, I would fully support kicking AFK people. 15/30 minutes, not so much. I play while I can, but when I have to do something like cooking dinner real quick, or if I had an especially large amount of Taco Bell for lunch, I wouldn't want to worry about having been kicked after 15min. Sometimes duty finder itself can take a little while and I may take that opportunity to get something else done while keeping a frequent eye on the screen.
Personally, I'd like to see SE implement a faster report system for gilsellers that are already populating the game as opposed to the reporting "form." That, plus quicker review times for such reports so that gilsellers could get booted (and muted) faster, allowing another slot for "good" players to fill.