Huge server load when using Hotlink Protection

I got 24 domains, and I did add them to Cpanels hotlink protecton like this.

http://domain.com x 24
http://www.domain.com x 24
http://subdomain.domain.com x 24

This create a huge server load, and the server becomes very slow.
But I need hotlink protection because alot of peoples is stealing my bandwidth.

Anyone know how I can do to use hotlink protection without getting this server load problems?

 

 

 

 

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