Answer
The domain is the set of the real numbers and $x\ne-5$ and $x\ne3$.
Work Step by Step
The denominator cannot be $0$, thus $x^2+2x-15\ne0\\x^2+5x-3x-15\ne0\\x(x+5)-3(x+5)\ne0\\(x+5)(x-3)\ne0$
Thus the domain is the set of the real numbers and $x\ne-5$ and $x\ne3$.
