A normal (regulation) 15-on-15 game has two, 40 minute halves. A Sevens rugby game, 7-on-7 lasts either 14 (two 7 minute halves) or 20 (two 10 minute halves) minutes. I believe you were watching a Sevens game, judging by the time.
The halfs are 40 min each at an adult level at high school level in Canada the halfs are 25 min And your right I don't know why it's not popular in Canada either its so fun to play