Let me put some light on it as my coder told me.
I use one IP for all sites so those requests were not by server but by the people visiting my three sites, they go down when I stop sites. It was not slow CPU causing them but slow CPU was not able to handle those requests and was showing errors in logs. One more thing I should add is that I changed my server from xeon to i5 coz i5 was cheap and it didn't come out good for me. Lucky for me the xeon server wasn't expired so I transferred file back to server installing Plesk and no errors in logs. Also the chev guru told me to go for xeon CPU when he showed me the server usage with htop tool and yes I did saw CPU going red. In xeon server there is no issue at all.
So its not the slow CPU but the traffic requesting the server. I'm not a pro so it was all my wrong interpretation from the start.