My sandboxes are small ... very small compared to your sites.
The fact I have multiiple versions of Moodle on that sandbox server means tweaks to mysql and apache (standard balancing act) needed.
Towards that end have found a tool like MySQLTuner but for apache ...
https://support.rackspace.com/how-to/using-the-apache-2-buddy-script-for-performance-and-stability/
'SoS', Ken