\[- 6\frac{7}{15} + \left( - 8\frac{3}{10} \right) =\]
\[= - \left( 6\frac{7}{15} + 8\frac{3}{10} \right) =\]
\[= - \left( 14\frac{14 + 9}{30} \right) = - 14\frac{23}{30}\]