To add the fractions \( \frac{4}{5} \) and \( \frac{5}{15} \), we first need to find a common denominator.
The least common multiple (LCM) of 5 and 15 is 15. Now, we can convert \( \frac{4}{5} \) to a fraction with 15 as the denominator.
\[ \frac{4}{5} = \frac{4 \times 3}{5 \times 3} = \frac{12}{15} \]
Now we can add \( \frac{12}{15} \) and \( \frac{5}{15} \):
\[ \frac{12}{15} + \frac{5}{15} = \frac{12 + 5}{15} = \frac{17}{15} \]
So,
\[ \frac{4}{5} + \frac{5}{15} = \frac{17}{15} \]
The answer in the form of \( \text{?/?} \) is \( \frac{17}{15} \).