CPU and RAM high usage

Dear Sugar experts,

We are experiencing an issue with our current Sugar 6.5.16 (Build 1082) installation on CentOS 6.7

CPU usage is always at 99.8% and memory usage is  below:

          total  used  free   shared buffers cached
Mem: 7.7G 7.5G 160M  96K      185M 1.3G

Processes that are consuming the most are mysqld and php ones.

Can you help us identify the issue or give us a hint on where to start looking at?