user: Question: Name the directed by for 15.15 viewers
Columns: ['Series #', 'Season #', 'Title', 'Directed by', 'Written by', 'Original air date', 'U.S. viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: [119.0, 1.0, '"Lost Boy"', 'John Polson', 'Byron Balasco, Greg Walker', 'September27,2007', '16.73']
SQL:

assistant: SELECT "Directed by" FROM "Table" WHERE "U.S. viewers (millions)" = '15.15';