Solution: The height of 15 layer is 42m, so 42÷ 15=2.8 (m) means the height of each layer is 2.8m, so it is concluded that11× 2.8 = 30.8. The speed of the elevator is 2 meters per second, so 30.8÷2= 15.4 (seconds) ≈ 16 (seconds).

A: It takes at least 16 seconds.