admin-ajax.php calls slowing down sites

Hi there

We have a few sites running Yop Polls, the problem we are having is that it appears Yop Polls requires connection to admin-ajax.php file. This is fine for a few times but when lots of users come to the sites it causes the sites to time out. You can see the load time of the site is increased significantly by calls to this script from Yop Polls https://www.webpagetest.org/result/170905_S7_73be7f19bd9dcd56ead5336bc948a447/2/details/#waterfall_view_step1

Is there someway we can limit this to make the site more efficient?

The page I need help with: [log in to see the link]