Slowness in web applications might be result of a wide range of underlying issues in the application code, client side, network or web server. Therefore, system administrators should analyze IIS logs, Failed Request Tracing logs, dump files, and HTTP.SYS logs to narrow down the issue.
If a web browser starts loading the web page but it never finishes loading it, look for the resources being loaded and the debug errors in F12 Developer Tools.
If the page has an iframe, try testing the page after removing the iframe. If it works without the iframe, then look for further leads to narrow the issue down.