How Can You Cook An Egg For Exactly 15 Minutes If All You Have Is A 7 Minute Hourglass And An 11 Minute Hourglass?

Hope she is old enough to use the stove.
1. Start both timers.
2 At the end of 7 minutes there will be 4 minutes left on the 11 minute timer.
3. Restart the 7 minute timer.
4. At the end of 11 minutes there will be 4 minutes left on the bottom of the 7 minute timer.
5. With 11 minutes gone by, restart the 7 minute timer by flipping it over with 4 minutes to go.
6. When the 4 minutes left on the 7 minute timer expires you have elapsed 15 minutes and your eggs are ready.

You will have to have quickly flipped the hourglasses. And, in my estimation the eggs will be way overdone.