Given:

Initial velocity, u = 15 m/s

Final velocity, v = 0 m/s

Time taken, t = 15 s

We can use the following kinematic equation to calculate the acceleration:

v = u + at

where

a = (v - u) / t

Substituting the given values, we get:

a = (0 - 15) / 15

a = -1 m/s^2

Therefore, the acceleration of the car is -1 m/s^2 (or 1 m/s^2 in the opposite direction of the car's motion).