rtMedia slowness and Varnish

When my site has rtMedia enabled, the homepage (which is only text and does not require being logged in) takes nearly 2 seconds to respond. As compared to other sites on the same host (Pantheon) that take 1/10th that time.

It seems like the sessions initiated by the plugin prevent varnish from caching the pages.

I would understand why logged in caching would be a problem… but I don’t understand why cache-busting sessions would be getting set on a plain text page for anonymous users.

Any insight on what’s going on? and ideas to improve it?