IIS 8.0 Webdav: >15 seconds wait time before logon screen appears

I use my own cloud with webdav to connect through a browser. It takes more then 15 seconds before the logon screen will appear.  This is very annoying.

HTML: ID="myElement" style="behavior:url('#default#httpFolder');" onclick = "myElement.NavigateFrame('https://myexampledomain.com/cloud','_blank')"

IIS 8.0 config is using SSL & Digest Authentication on a Windows Server 2012.

Browser: IE10 on Windows 8 and Windows Server 2013.

Any hints?