user: Question: When 15 is the number overall what is the original air date?
Columns: ['No. overall', 'No. in series', 'Title', 'Director', 'Writer', 'Original air date', 'Production code']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'real']
Sample row: [9.0, 1.0, '"Episode 1"', 'Peter Lydon', 'Julie Rutterford', '13March2002', 201.0]
SQL:

assistant: SELECT "Original air date" FROM "Table" WHERE "No. overall" = 15.0;