CREATE TABLE table_73004 ("No. overall" FLOAT, "No. in series" FLOAT, "Title" CLOB, "Director" CLOB, "Writer" CLOB, "Original air date" CLOB, "Production code" FLOAT)

When 15 is the number overall what is the original air date?
SELECT "Original air date" FROM table_73004 WHERE "No. overall" = '15'
SELECT "Original air date" FROM "table_73004" WHERE "No. overall" = '15'