There was enough water in the great deep to flood the Earth 1,200 km deep. 15 cubits was when the crew of the ark stopped taking soundings. Mount Everest formed 101 years AFTER Noah's flood during Peleg's tectonics.
August 3rd
Noah’s Math
Some folk think that they can use 19th Century Uniformitarianism to show that Noah's flood didn't happen. We hate to break it to you, but, this is the 21st Century.