So how much do you weigh then? Edit: scratch that I've just seen that you're 86kg.
I've just tried this out - I weigh 80kg's and used 2x20kg DB's and knocked out 32 decent reps in a minute - tough going I can tell you.
I have very little in the way of endurance and have spent most of my time doing lower volume higher intensity weights and BW gymnastic isometrics etc. Only recently have I done serious volume and am on week 5 of 6 of GVT so I think that's probably helped, otherwise I reckon I'd have done 20 or less.
I'm 74kg and I cannot get past 10kg dumbbells at 15 reps. My arms collapse as I try for 20 reps each time after I recover for 2 - 3 minutes. I couldn't even imagine trying 20kg