high load average on KVM VM web servers

I have a server with KVM libvirt and OVS. Debian 8.6. I am currently running 2 web servers with installed nginx+php5-fpm on VM . HAProxy is used to balance requests and installed on KVM virtual machine. PHP sessions are stored on memcached on another VM. Web site is written in Yii2 framework. Every 15 minutes or 30 minutes the load average of web servers are increasing untill 200-300. The capacity of Database is around 1GB. The type of site is media. A lot of contents and live tv channels. How to solve this problem ?