With training and when you are expecting to go into the sea yes obviously you can swim 20 miles across the English channel but all the cardiac arrests from cold water shock and general panic in the first 15 seconds bring the average down. The rule of 3 makes it easier to remember; they are approximate average numbers which are meant to drive the point home which is to wear a life jacket. We would prefer to find you shivering on a beach than face down in the sea.

This has nothing to do with trained cold water swimmers. Your figure is just completely off. 15C water does not kill people in three minutes. It does not cause cardiac arrest. An average person could last hours at that temperature. See the well cited link I provided.

Lying to people to try and encourage safe behaviour isn't wise. The truth is good enough.

he did say what brings that number down (it's an average). and yes, jumping/falling into cold water can lead to shock/cardiac arrest