To add the fractions \(-\frac{8}{15}\) and \(\frac{4}{15}\), since they have a common denominator, you can simply add the numerators:
\[ -\frac{8}{15} + \frac{4}{15} = \frac{-8 + 4}{15} = \frac{-4}{15}. \]
So, \(-\frac{8}{15} + \frac{4}{15} = -\frac{4}{15}\).