Hi there,
with CentOS 7 and Apache 2.4, the Prefork MPM will be used by default, but with Plesk 12.5 it´s mpm_event.
Where is the configuration file for mpm_event with Plesk 12.5? I have only found a file for prefork:
cat /etc/httpd/conf.d/mpm_prefork.conf
# prefork MPM
# StartServers...