admin-ajax returning 0

Question-
We have WordPress Multisite (subdomains) with domain mapping, nginx server. Load times seems to be extremely slow even though we have a very good, fast server.
When I go to NewRelic there has been a heavy load on /admin-ajax.php
When I go to our url.com/wp-admin/admin-ajax.php
it goes to a page with only a 0
Is this a good thing or a bad? If it is bad how do I fix it?