15 minutes is a good ball park for a 1 pass WTG shave with a razor and soap I know well.
On weekends or offdays, I spend more time and tend to use "lesser used" razors and soaps... I take my time and enjoy these shaves much more. I also tend to use two razors.... one I've recently honed as a test run / primary razor and have one on standby as an "emergency backup spare" in case my honing of the primary was sub-par.