Slow calendar page loads

I’ve been getting very slow page loads on our calendar. It’s common for the calendar page to take 5-15 seconds to load/cycle months. The rest of the site loads reasonably fast.

I’ve had this issue for a while, but it seems particularly bad at the moment. I suspect our hosting company is to blame as it’s a rather low end, virtual server plan – but I wanted to see if anyone had any ideas I hadn’t tried yet before abandoning them.

So far, I’ve tried the following – none of which have helped:
1) Reinstalling the events manager plugin and wpfullcalendar plugin, as well as resetting their settings.
2) Various caching and performance addons (w3 total cache, hypercache, autooptimize, a2optimize, etc)
3) Disabling every plugin except events manager and wpfullcalendar and reverting to the default WordPress theme. Also disabling wpfullcalendar and using the default calendar view is equally slow.
4) Copied our site & sql database to a local test server (it seems to run much faster there, which is what has me believing the virtual hosting is to blame)
5) Using Chrome’s performance analysis, it shows admin-ajax.php taking the most time, but the various guides I’ve followed on how to optimize that haven’t helped any.
6) Purging old events and the page cache
7) Added the “Use Google Libraries” plugin as suggested by EventsManager in their settings/performance optimization page

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