Answer:
It will take 15 seconds.
Step-by-step explanation:
Since the acceleration due to gravity is a constant, the motion is exactly symmetric. This means that the time an object lasts to travel a distance when it goes upwards, is the same time in which it will cover the same distance downwards. So, as the object reaches its maximum height in 15 seconds from a point 2 meters above the ground, it will take another 15 seconds to go from the highest point to that altitude.