72 minutes
1 1/2 hours
I think it was a convenience, as people began to need smaller time intervals than 1 hour to agree on. Before mechanical clocks, if you had to agree on a meeting time with someone, the closest you...
60 minutes = 1 hour
There are 60 minutes in one hour and 120 minutes in two hours, so 115 minutes is equal to one hour and 55 minutes.