Hour Glass Puzzle

#1

You have two hourglasses: a 7 minute one and a 11 minute one.
Using just two hourglass, accurately time 15 minutes.

#2

You start both the jars.
After 7 minutes, the 7 minute jar gets empty, you flip it and it again starts emptying.
Now at 11 minutes , you know the 7 minute jar would end in 3 minutes. But if you flip it, it will empty in 4 minutes, thus after 11 mins you flip it, and no when it gets empty we know that it’s 4 minutes more.

Thus 11+4