user: Question: Which Date has a Winning score of −15 (71-69-68-65=273)?
Columns: ['Date', 'Tournament', 'Winning score', 'Margin of victory', 'Runner-up']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['21 May 1989', 'Lancia Italian Open', '−15 (71-69-68-65=273)', '1 stroke', 'Sam Torrance']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Winning score" = '−15 (71-69-68-65=273)';