The 2015 World's Best Racehorse Rankings, sponsored by Longines was the 2015 edition of the World's Best Racehorse Rankings. It was an assessment of Thoroughbred racehorses issued by the International Federation of Horseracing Authorities (IFHA) in January 2016. It included horses aged three or older which competed in flat races during 2015. It was open to all horses irrespective of where they raced or were trained.