I'm optimising a website, and the problem I'm facing with now is server related. During page load, there are about 40-50 requests sent to server (depending on the page), and in every case, server hangs for about 5-6 seconds on a certain file (images mostly, cause css and js is getting merged), or two or three.. take a look at firebug screenshot to get a better idea what I'm talking about
https://i.stack.imgur.com/aDhih.png
(there are 90 requests here cause js and css are not merged).
website is Bigelow Chemists . Any idea what might be causing this. I can take a deeper look, I just need a hint at what might be the cause for such behaviour. Thanks