CREATE TABLE table_54304 ("Date" TEXT, "Score" TEXT, "Set 1" TEXT, "Set 2" TEXT, "Set 3" TEXT, "Total" TEXT)

What is the Date with a Set 3 with 15 6?
SELECT "Date" FROM table_54304 WHERE "Set 3" = '15–6'
SELECT "Date" FROM "table_54304" WHERE "Set 3" = '15–6'