```
Potential Energy = mass × gravity × height
```
Where:
* Potential Energy is measured in Joules (J)
* mass is the mass of the ball in kilograms (kg)
* gravity is the acceleration due to gravity (approximately 9.8 m/s²)
* height is the maximum height reached by the ball in meters (m)
Given that the ball is thrown 15 meters into the air, the maximum height reached by the ball is 15 meters.
Let's assume the mass of the ball is 0.5 kilograms.
Plugging in the values, we get:
```
Potential Energy = 0.5 kg × 9.8 m/s² × 15 m
```
```
Potential Energy = 73.5 Joules
```
Therefore, the maximum potential energy of the ball at a height of 15 meters is 73.5 Joules.
