"No one will ever beat that time!" I said, two PBs ago.
The fastest possible kettle kill I've had the opportunity for is 15 minutes.
I've tried multiple strategies but it seems that the default class set seems to be the fastest overall. The wizard could be replaced by a fighter for a slight increase in speed, but it'd be a slower run if you got drops like a hand axe or chain mail (which you'd use, then sell) that need to be identified.
Best drop I've ever received was two hand axes from a group of 8 bandits (!), acolytes can also drop maces and chain mail.
You can trick the game into giving you more treasure chests by saving on a spot that normally gives you a chest, resetting, and then getting into a combat on or adjacent to that space. Dunno why it works, but it does. Chests don't really give you much more gold per minute due to the time it takes to disarm and open them, but they can speed things up if you get the right item drops early. It's still a good idea to go for chest combat because it is a guaranteed encounter, especially early on.
Used J version due to faster resets.