CREATE TABLE table_70715 ("Dance" TEXT, "Best dancer ( s ) " TEXT, "Best score" FLOAT, "Worst dancer ( s ) " TEXT, "Worst score" FLOAT)

What's the best average score with a bad score of 15?
SELECT AVG("Best score") FROM table_70715 WHERE "Worst score" = '15'
SELECT AVG("Best score") FROM "table_70715" WHERE "Worst score" = '15'