When I want to do a quick demo I don't have people play a game. Instead, I take them through the mechanics. I start with a description of army building (point-based) and how players take turns deploying their armies and giving standing orders. I explain how standing orders, with command actions, are the command and control system of the game and how this will give you a sense of being a general in charge of an army rather than a hive mind in charge of all of your troops. Then I show how movement works by having a couple of units advance towards each other until they are within final rush range, at which point I show final rushing and go into combat. I'll usually add in a command card to combat but have the players roll their dice and mark off damage. From there I show how the hits get marked off and how color determines fighting strength and morale. Then I do a quick overview of pinching, flanking, etc., so that they see that this is a game of maneuver and strategy, not just dice-rolling.
That can be done in 10-15 minutes, and usually some of the folks will want to dig in for a full game, in which case I'd give them quickstart armies and let them go.
