Script lag depends on many things.
What script are you using first of all? Some scripts may not be scripted as well so take longer to execute.
Another reason is if you run VC on the same computer as the scripts, on some low end machines, vc will take priority and lag the scripts out.
Also you have to take into consideration the network lag between scripts and the server. if the scripts are hosted on the other side of the worl to the server then it will respond slower.
To be honest there are many differant reasons why scripts would lag. These are probably the most common though
