Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
Which MotoGP winner has a 250cc winner of marco simoncelli, and a Round of 15?

### Inputs:
table_name: table, columns: ['Round', 'Date', 'Grand Prix', 'Circuit', '125cc winner', '250cc winner', 'MotoGP winner', 'Report']

### Response:
SELECT MotoGP winner FROM table WHERE 250cc winner = marco simoncelli AND Round = 15