If the purpose is after-sales support, then no, 15-20 minutes is not unheard of.

My division has a goal of 80% of the calls answered in 2 minutes or less. And this is not done by pushing the length of the call times either. It's taken delicate shift balancing, plus some other factors, but it does happen most of the time. And our customers appreciate it. I've caught several people not even ready for the call because they thought they would be waiting