Given the definitions of $f(x)$ and $g(x)$ below, find the value of $g(f(-3))$.
$\begin{array}{l}
f(x)=-x-7 \\
g(x)=2 x^2-3 x+15
\end{array}$
$\begin{array}{l}
f(x)=-x-7 \\
g(x)=2 x^2-3 x+15
\end{array}$