By Joice Alves and Gertrude Chavez-Dreyfuss LONDON/NEW YORK (Reuters) - The yen plunged to a fresh 15-year low against the euro on Friday after the Bank of Japan (BOJ) kept ultra-low interest rates and forecast that inflation will slow later this year, in contrast with the European Central Bank's (ECB) rate hike on Thursday. The Japanese currency also fell against the dollar, dropping to a