- Plesk 12.5 for Linux
- Plesk Onyx for Linux
High CPU and memory usage by Apache.
Apache module is used to serve PHP. It is the slowest handler available.
Switch websites to FastCGI by Apache or, better, to PHP-FPM by Apache
If the CPU usage is still high, consider installing and switching to Nginx: Tools & Settings > Services Management > Reverse Proxy Server (nginx)
Note: nginx does not support .htaccess rules