Config xcache apache

im use centos 6.8 & Apache/2.2.15

When I install xcache
I get the following error

PHP Warning:  Module 'XCache' already loaded in Unknown on line 0
PHP Fatal error:  XCache: create entries OOM in Unknown on line 0
PHP Fatal error:  XCache: failed init variable cache in Unknown on line 0
PHP Fatal error:  XCache: Cannot init in Unknown on line 0
PHP 5.4.45 (cli) (built: Jun  9 2016 12:28:19)
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2014 Zend Technologies
    with XCache v3.1.1, Copyright (c) 2005-2014, by mOo
    with XCache Optimizer v3.1.1, Copyright (c) 2005-2014, by mOo
    with XCache Coverager v3.1.1, Copyright (c) 2005-2014, by mOo

What can I do to fix this error?

I got a question
How do I configure Apache to get the highest performance?
6 GB of RAM
4-core CPU
esx


at the moment
prefork
timeout 60
Keepalive on
MaxKeepAliveRequests 150
KeepAliveTimeout 10
StartServers 20
MinSpareServers 25
MaxSpareServers 55
ServerLimit 4000
MaxClients 500
MaxRequestsPerChild 2000
The server is just a website joomla

With special thanks

It takes time to be loaded pages
And CPU usage is high