Well, unfortunately for you and anyone else that just wants to 'get in, play for 15 minutes' and get out, this game was not developed with you in mind. It was developed for those people who enjoy playing games like Civilization, Hearts of Iron, Galactic Civlizations, Master of Magic and any other turn-based strategy game. Games of that sort almost NEVER last less than even a single hour and generally take anywhere from 3 to 30 hours to play. You're actually the very first person to mention anything negative about long game times on these forums, that I've seen.
People that play these games LIKE the fact that they take a long time because there's a sense of 'accomplishment' in raising your civilization from the ground up, making alliances with enemies and neighbors, building a military empire, and coming out victorious in the end. Even if you lose a close match there's a sense of achievement in having built and done what you could to win.
So, this game could still turn out to be a crap game but it won't be because they didn't incorporate a 15-min multiplayer game mode. It would be for such things as the diplomacy system is crap, or there's a huge imbalance in units, or the gameplay just stinks. However, with Stardock's track record, namely Galactic Civilizations II, I seriously doubt they will make a crap game out of Elemental.