I have an m3.xlarge EC2 instance that I updated to PHP 5.5.11 today.
With this update, it overwrote php55-pecl-apc with
You also have
opcache.consistency_checks=1
Which according to the docs says will slow down performance. Turn that off.
opcache.consistency_checks integerIf non-zero, OPcache will verify the cache checksum every N requests, where N is the value of this configuration directive. This should only be enabled when debugging, as it will impair performance.