Rahil had 15 \( \frac{5}{8} \) / petrol in the vehicle's tank at the beginning of the journey. At the end of the journey only 3 \( \frac{1}{8} \) / petrol was left in the fuel tank. What part of the initial quantity of petrol was consumed during the journey?
\( \frac{3}{4} \)
\( \frac{9}{10} \)
\( \frac{5}{6} \)
\( \frac{4}{5} \)