\[a = \frac{2}{5}:\]
\[- 15a^{2} = - 15 \cdot \left( \frac{2}{5} \right)^{2} = \frac{- 15 \cdot 4}{25} =\]
\[= - \frac{12}{5} = - 2\frac{2}{5} = - 2,4.\]