We can improve ajax response by following way.
1)Optimization in ScriptManager
-we also got about a 50% download speed improvement by only having one request.
<ajax:ToolkitScriptManager ID="SM1" runat="server" EnablePageMethods="true" EnablePartialRendering="true" ScriptMode="Release"
There is another property in ScriptManager named EnablePartialRendering, it gets or sets a value that enables partial rendering of a page, which in turn enables you to update regions of the page individually by using UpdatePanel controls.
So, if we using the UpdatePanel in the page, we must set this property to true, conversely, if the UpdatePanel is not using in our page, it would be better that we set the EnablePartialRendering to false.
2)Optimization in Web.config
To optimize the ASP.NET AJAX in our web application, first of all, we need to make sure the Compression and Caching is enabled in our web.config.
-The Caching will saving almost 95% of the network traffic in the second time we request the page.
<scriptResourceHandler enableCompression=“true” enableCaching=“true”/>
These above changes very well worked for me .
i hope this will help you too.