Huge delay to post a comment

Hi! I run a mid-sized blog (~3k comments/month) and noticed that Nginx Helper adds a huge delay when someone sends a comment.

From clicking on “Post” button to see the comment, it takes ~13 seconds.

I ran a test in an staging environment, without Nginx Helper, and it took 2~3 seconds to publish a comment.

Is there anything wrong with my installation? Any ideas about how to reduce this delay?