\[\frac{5 - \sqrt{5}}{\sqrt{15} - \sqrt{3}} = \frac{\sqrt{5}\left( \sqrt{5} - 1 \right)}{\sqrt{3}\left( \sqrt{5} - 1 \right)} =\]
\[= \frac{\sqrt{5}}{\sqrt{3}} = \frac{\sqrt{5} \cdot \sqrt{3}}{\sqrt{3} \cdot \sqrt{3}} = \frac{\sqrt{15}}{3}.\]