SELECT
   compositions.composer, compositions.composition, compositions.date, compositions.performedBy
FROM
   compositions
   INNER JOIN
   (SELECT composer
    FROM compositions
    WHERE
      composer IN (
         SELECT composer FROM compositions
         GROUP BY composer
         HAVING COUNT(1) < 15
      )
    ORDER BY RAND()
    LIMIT 1) AS RandComposer
ON
   compositions.composer = RandComposer.composer
ORDER BY compositions.composition