Slow tracker performance

Hi

I have Piwik 1.9.1 , this is stock version ( we have tweaked few php codes, just renamed some files). I am facing slowness issue. It took almost 6-9 second to load just tracker , whereas google analytics script got loaded in max 600ms. Please suggest what to do.

I am using Server:Apache/2.2.3 (CentOS), and piwik 1.9.1 stock version.

Upgrade right now to 2.7.0! cheers