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_67 (fixtures INTEGER, round VARCHAR, clubs_involved VARCHAR)
### Question:
In the sixth round, what is the sum of fixtures when there were more than 15 clubs involved?
### Answer:
SELECT SUM(fixtures) FROM table_name_67 WHERE round = "sixth round" AND clubs_involved > 15