Every post back in the form is taking long time when several update panels is also used in ASP.Net

I have a big form in which i have almost 10 update panels. some are having updatemode = conditional and others are always. Now by default when that page is opened i only show one dropdownlist.When that project dropdownlist (from which i populate the rest of the elements in my page) value is changed by user it takes long time to load the other elements. Also the other gridview which is also surrounded by update panel and mode in conditional takes long time to show edititemtemplate controls in edit mode. 

I am unable to trace the reason behing delay. Few days ago it was working fine and fast but now it is slow.