NEW YORK--(BUSINESS WIRE)--Fitch Ratings has assigned the following ratings for Agate Bay Mortgage Trust 2015-4: $166,094,000 class A-21 initial exchangeable certificates 'AAAsf'; Outlook Stable; $11,073,000 class A-22 initial exchangeable certificates 'AAAsf'; Outlook Stable; $44,291,000 class A-23 initial exchangeable certificates 'AAAsf'; Outlook Stable; $15,387,000 class A-24 initial exchangeable certificates 'AAAsf'; Outlook Stable; $236,845,000 class A-X-1 notional certificates 'AAAsf'; O