user: Question: What is the Heat of the Player with a Rank of 18 or less and Result of 55.15?
Columns: ['Rank', 'Heat', 'Name', 'Nationality', 'Result']
Types: ['real', 'real', 'text', 'text', 'text']
Sample row: [1.0, 3.0, 'Melaine Walker', 'Jamaica', '54.46']
SQL:

assistant: SELECT "Heat" FROM "Table" WHERE "Rank" < 18.0 AND "Result" = '55.15';