My son has always been a short nurser too, except when he was a newborn.
Now, at 10 months, he will go anywhere from 2-4 hours between nursing sessions, and only nurses for 10 min MAX. As babies age, they can get super efficient at emptying the breast, so it's quite possible he's getting a full feed in only 5-15 min.
He never really exhibits the classic hunger cues either. I feed on demand though, so whenever he gets fussy or upset I offer the breast, whether it's been 3 hours or 3 minutes since his last feeding. If he's hungry, he'll eat, and if he's not, he'll refuse.
It sounds like he's doing fine, gaining well and meeting milestones. As long as he is having plently of wet diapers each day (6+), you can rest assured that he's getting enough milk. If it's coming out, it has to be going in!
