Answer
$-4$
Work Step by Step
Use the rule $a-b=a+(-b)$ by replacing $\color{blue}{-15}$ with $\color{red}{+(-15)}$:
$11\color{blue}{-15}=11\color{red}{+(-15)}$
Since $|-15|>|11|$, subtract $|11$ from $|-15|$, then copy the sign of $-15$ to obtain:
$\begin{align*}
11+(-15)&=-(|-15|-|11|)\\
&=-(15-11)\\
&=-4
\end{align*}$
