To add the fractions \(-\frac{8}{15}\) and \(\frac{4}{15}\), you can simply combine the numerators since the denominators are the same:
\[ -\frac{8}{15} + \frac{4}{15} = \frac{-8 + 4}{15} = \frac{-4}{15} \]
So, \(-\frac{8}{15} + \frac{4}{15} = -\frac{4}{15}\).