To solve the equation \( 15 = \frac{x + 2}{-3} \), we can start by eliminating the fraction. We'll multiply both sides of the equation by \(-3\):
\[ 15 \cdot (-3) = x + 2 \]
Calculating the left side:
\[ -45 = x + 2 \]
Next, we isolate \( x \) by subtracting \( 2 \) from both sides:
\[ -45 - 2 = x \]
This simplifies to:
\[ x = -47 \]
So, the solution is:
\[ \boxed{-47} \]