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_21172539_1 (original_air_date VARCHAR, no_in_season VARCHAR)

### Question ###
What date did episode 15 of the season originally air?

### Accurate SQL ###

SELECT original_air_date FROM table_21172539_1 WHERE no_in_season = 15