Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_73004 ( "No. overall" real, "No. in series" real, "Title" text, "Director" text, "Writer" text, "Original air date" text, "Production code" real )

### Question ###
When 15 is the number overall what is the original air date?

### Accurate SQL ###

SELECT "Original air date" FROM table_73004 WHERE "No. overall" = '15'