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

### Instruction:
What was the highest lap count for Walker Racing with a grid larger than 15?

### Inputs:
table_name: table, columns: ['Driver', 'Team', 'Laps', 'Time/Retired', 'Grid', 'Points']

### Response:
SELECT MAX Laps FROM table WHERE Team = walker racing AND Grid > 15