Answer
$\frac{1}{x^{15}}$
Work Step by Step
When an exponential expression is raised to a power, multiply the exponents: $$(x^{(-5)})^{3}$$
$$=x^{(-5\times3)}$$
$$=x^{(-15)}$$
A expression with a negative exponent can be simplified by moving the base from the numerator to the denominator (or vise versa):
$$=\frac{1}{x^{15}}$$