That is a bit out of scope of this Support Community, but you could try a Wordpress caching plugin or a caching server like varnish.
I just checked your card again, seems your server was now fast enough, maybe this was only some hickup. But I noticed another problem, you are defining two different card types in one page:
<meta name="twitter:card" content="summary_large_image">
and
<meta name="twitter:card" content="summary">
which seems to make it to not work properly. Please check the config again and make sure you only define one card type on a page.