user: Question: What couple averaged 15.5?
Columns: ['Rank by average', 'Place', 'Couple', 'Total points', 'Number of dances', 'Average']
Types: ['real', 'real', 'text', 'real', 'real', 'text']
Sample row: [1.0, 1.0, 'Nicole & Derek', 468.0, 17.0, '27.5']
SQL:

assistant: SELECT "Couple" FROM "Table" WHERE "Average" = '15.5';