Final answer:
Raul must rent 15 bicycles, one for each of his 15 friends, to ensure that each friend has the same bicycle.
Step-by-step explanation:
Raul needs to rent a bicycle for each of his 15 friends to ensure that each friend has the same bicycle. Therefore, Raul needs to rent 15 bicycles. This problem is straightforward and involves basic multiplication or a one-to-one match; one bicycle per friend. There is no need for complex calculations or additional information to determine the answer.