Welcome. You are playing Dominion wrong.
Actually, I think you will find that even with the standard rules, as you get better and players become more aware of how piling out affects the game, 3 and 4 player games will take longer. When I play 3 or 4 player games, it's common to have at least one game in the evening last at least 45 minutes.
Also, remember that a great thing about Dominion is that because the game is over fairly quickly, someone who gets bad luck (or for whatever reason falls way behind) doesn't have to suffer through 30 more minutes of not having a chance to win at all. The game ends, you shuffle up, and play again!