user: ### NOW ANSWER:
Question: When has a Tie no of 15?
Columns: ['Tie no', 'Home team', 'Score', 'Away team', 'Date']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['1', 'Chester', '1–0', 'Barnsley', '18 December 1979']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Tie no" = '15';