iPhone 6s waterproof [video]
youtube.com
youtube.com
I'd also want to see if those phones worked a week or two after the test to ensure that their insides didn't corrode after their submersion and subsequent exposure to air.
If this is indeed waterproof, I'd also want to know about how deep it can go.
The depth is a major issue. Water pressure is the real devil for water resistance. I'd like to see someone test the 6s in a pool.
The second thing is about water pressure, which you highlighted as the key factor in water resistance.