Bring a dish of frozen lasagna put it in microwave at the beginning of the session in 15 minutes later it should be done. This way you get the whole 15 minutes and don't get cheeted.
There's cheaper ways to heat your lasagna. Most gas stations have a free microwave!
15 minutes in the micro and you will end up a square hockey puck. You might have better luck with an egg timer. If 15 minutes is all you need then maybe you should just stick with your hand