Sideband connection - takes few seconds to get resonse

Hi, I've created the iRule that establishes sideband connection to make a decision what pool the original HTTP request to be sent according to the response data from the sideband virtual server. It takes ~3-5 seconds until the response from sideband VS came. If i simulate sideband HTTP request from, let say, my workstation using fiddler, the response has no delay.

Any idea what the problem could be?

Thanks Sergey