If one side is stronger than the other, yes. If you put a good team versus an average in a DotA match, the game is over in less than 30 minutes as well.
If you finish in 30 minutes I guess you're around level 15 and without any artefacts or high-tier items. Just for the record, what are the 'general' team scores, in warrank and hero-kills- and are buildings usually destroyed on both sides, or is one side barely touched while the other is crushed? Besides, are you guys talking about full, conquest mode, or one of the mini-games?