admin-ajax.php slow loading

It also makes several calls to the same file. Several links placed on the same source code.

Check my site in pingdom tools: https://www.hostingroup.com/blog/

You will need to contact your host to fix this.

Sounds like you are on a slow or shared server

No, the server is fine, pages load in 1 second, the problem is that the file the longer it takes to load is the admin-ajax.php well be called many times in the source code.

Please make a test in pingdom to check what I say.