text: Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
  ### Context:
  CREATE TABLE table_name_81 (grid INTEGER, time_retired VARCHAR, laps VARCHAR)
  ### Question:
  what's the average grid that has a time/retired piston and laps smaller than 15?
  ### Answer:
  SELECT AVG(grid) FROM table_name_81 WHERE time_retired = "piston" AND laps < 15