The correct answer is C. 20 sec.
The equation for the distance traveled by an object with a constant acceleration is $d = v_0 t + \frac{1}{2} at^2$, where $v_0$ is the initial velocity, $t$ is the time, and $a$ is the acceleration. We are given that $v_0 = 2 \text{ m/s}$, $a = -0.1 \text{ m/s}^2$, and $d = 1.5 \text{ m}$. Substituting these values into the equation, we get $1.5 = 2 t + \frac{1}{2} (-0.1) t^2$. Solving for $t$, we get $t = 20 \text{ sec}$.
Option A is incorrect because it is twice the correct answer. Option B is incorrect because it is three times the correct answer. Option D is incorrect because it is half the correct answer.