When 15 is the number overall what is the original air date?
CREATE TABLE table_73004 (
    "No. overall" real,
    "No. in series" real,
    "Title" text,
    "Director" text,
    "Writer" text,
    "Original air date" text,
    "Production code" real
)
SELECT "Original air date" FROM table_73004 WHERE "No. overall" = '15'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: When 15 is the number overall what is the original air date? ### Input: CREATE TABLE table_73004 (
    "No. overall" real,
    "No. in series" real,
    "Title" text,
    "Director" text,
    "Writer" text,
    "Original air date" text,
    "Production code" real
) ### Response: SELECT "Original air date" FROM table_73004 WHERE "No. overall" = '15'