It looks like this PR made a change to the proxy code which removes the port number from the proxied HTTP request if the port number matches the default port for the schema. In 3scale 2.14, APIcast would connect to a proxy server and issue a request (for example) to http://www.example.com:80/foo, but in 2.15, the same request now will be for http://www.example.com/foo (no port number since the default port for http is 80).

Please update the 2.15 release notes to include this change.