Let’s take v as 0 bcuz the ball will be at rest at the top of its path
u is 15 m/s
And g which is acceleration due to gravity is 10m/s square
So
v square - u square = 2gh
0 - 15 square = 2 x -10 x h
- 225 = -20h
h = 225/20
= 11.25 m
s which is distance equals 11.25 m
So time taken will be
Distance/speed
Which is 11.25/15
Which is 0.75
So it’ll take 0.75 seconds.