\[\left( - \frac{5}{6}a^{- 9}b^{- 5} \right)^{- 3} \cdot \left( 6a^{15}b^{6} \right)^{- 2} =\]
\[= \left( - \frac{6}{5} \right)^{3}a^{27}b^{15} \cdot \left( \frac{1}{6} \right)^{2}a^{- 30}b^{- 12} =\]
\[= \frac{- 6^{3}}{5 \cdot 6^{2}}a^{- 3}b^{3} = - \frac{6b^{3}}{5a^{3}}\]