It's not really the number of database fields that matters here, but rather the additional size of the data in all of those fields.

How large will they be? Multiply by the number of database entries which have data in those fields, and there's your answer.

Eg. 15 fields, averaging 300 bytes of new data, with perhaps 400 tracks tagged with the new fields, equals 300 * 400 bytes or 12K. Not significant.

But if all 15000 tracks had 300 extra bytes, then this might (or not) trigger memory troubles on some players.