\[\sqrt{16 - 2\sqrt{15}} - \sqrt{19 - 4\sqrt{15}} =\]
\[= \sqrt{\left( \sqrt{15} - 1 \right)^{2}} - \sqrt{\left( \sqrt{15} - 2 \right)^{2}} =\]
\[= \sqrt{15} - 1 - \left( \sqrt{15} - 2 \right) =\]