15 men over 1.5 hours,that works out at 6 mins each.Not for me thanks.
You've made a schoolboy error in your calculation!
15 cocks / 3 holes = 5 Rounds of 18 minutes each!
I am sure you will have a percentage who's firearm is fixed with a hair trigger, thereby possibly increasing orifice access time for those who can hold off a bit!
Might bump the cock to hole ratio in your favour! I recon 20 minutes per cum tunnel @ £60 is a bit of a bum deal! 2/3 of the blokes would have to be up for some DP!
My sadistic maths teacher in school was right about maths being useful!