CREATE TABLE table_name_51 (tyre VARCHAR(255), chassis VARCHAR(255), rounds VARCHAR(255), engine VARCHAR(255))
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"