Table schema:
CREATE TABLE table_name_51 (tyre VARCHAR, chassis VARCHAR, rounds VARCHAR, engine VARCHAR)

Question: When the engine Ford Cosworth DFV 3.0 v8 has a chassis of m23 and in rounds 14-15, what is its Tyre?
SQL: SELECT tyre FROM table_name_51 WHERE rounds = "14-15" AND engine = "ford cosworth dfv 3.0 v8" AND chassis = "m23"