Yep, it's tough work - but I'm getting fitter!
I generally do the 15 miles in 52-53 mins in the morning (lovely going down hill ) and then 58 mins to just over an hour on the way home. I'm looking forward to getting a road bike as I'm hoping it will make those hill climbs a little bit more bearable on the way home.
The A21 is pretty good, lots of traffic lights around Bromley/Lewisham/Catford which can be a pain and add minutes on the commute - but not too bad. Some fairly bumpy stretches of road too!
Been doing the A21 for the past 7 years now.. I think I know every single little bump & potholl that the A21 has