Plugin slowing down the website

I already have contact with you guys on Skype, but I am not receiving a reply anymore. Therefore I am now trying it in ‘the open’.

We use Contact Form 7 and vTiger CRM and this plugin is the perfect piece of this puzzle.
Every lead by Contact Form 7 is being logged in vTiger exactly the way I want it. Really, it’s great!

BUT, there is only one issue.
This plugin is slowing down our website too much.
When you visit our website you see the page for a second, you get a white screen, have to wait a few seconds and then the page is shown. This problem is not around when I deactivate this plugin.

Therefore, this plugin is not activated at the time, which is a shame, since we already paid for it and we really want to use it.

Since I am not getting any reaction by Skype AND this problem is going on for too long now I am sending this post.

If someone might know WHAT I can do solve this problem, please let me know.