For this case what we should do is fill in the blank with the correct verb.
The correct verb for this case is:
Tener
The conjugation time is simple present.
The conjugation will be done for the third person singular.
Completing the sentence in Spanish we have:
Mi hermano tiene 15 años
The translation of the sentence in English is:
My brother is 15 years old
Answer:
"Tiene"
Mi hermano tiene 15 años