Translation:Fifteen people play on the team.
"Progress in Irish" shows cúig bhó dhéag (15 cows) in the section about numbers with a noun, but cúig fhear déag (15 men) in the section on personal numbers. Should there be a difference or not? (Not the first time PII would be different or slightly unclear on this topic - also in the personal numbers section is the statement "The personal numbers take the singular of the noun" which seems not to be true in general, but only when the genitive plural = nominative singular.)
Numbers seems to have lots of complex rules!
According to the entry for déag in the FGB,
After noun preceded by cardinal or ordinal number; when preceded by cardinal, lenited after sg. noun ending in vowel and after pl. noun ending in slender consonant
duine and bó end in vowels, so déag is lenited. fear doesn't so déag isn't lenited.