You turn the 7 minute one and the 11 minutes one at the same time. When the 7 one finishes, turn it again. When the 11 one finishes, you know that 4 minutes have passed, with 4 minutes to get to the desired 15, all you need to do now is turn the 7 minute hourglass again since it counted 4 minutes, and when it runs out it'll be exactly 15 minutes.
The Poisoned Dinner
Riddle:
Two girls ate dinner together. They both ordered iced tea.
One girl drank them very fast and finished 5 of them while the second girl finished just one.
The girl who drank one died while the other survived.
All the drinks were poisoned.
How did the girl who drank the most survive?
Two sisters we are, one is dark and one is fair,
In twin towers dwelling we're quite the pair,
One from land and one from the sea,
Tell us truly, who are we?
A woman shoots her husband, then holds him under water for five minutes.
A little while later, they both go out for dinner and enjoy it very much.
How can this be?
I usually go with a special beef, I'm a green vegetable, like a leaf. I'm a yummy addition to your St. Patrick's Day dinner. If you eat me a lot, you might even get slimmer. What am I?