Error in Ajax?

Hi,
I’m improving my website performance, and in Pingdom I’m having only one more unsolved thing:
http://www.mysiteurl.com/?_wpcf7_is_ajax_call=1&_wpcf7=163&_wpcf7_request_ver=1378567979793
This url brings me about from 2.5 to 4.5 secs. Can anyone pls help me? Is this code necessary? How do I remove that?
Thanks in advance

http://wordpress.org/plugins/contact-form-7/