As @andypiper already pointed out, your site takes way too long until it sends a response, I just checke it and it takes about 19 seconds:
time_namelookup: 0,005
time_connect: 0,243
time_appconnect: 0,000
time_pretransfer: 0,243
time_redirect: 0,000
time_starttransfer: 17,107
----------
time_total: 19,105
This is way too long, it should be something about 2 seconds! You might want to try out a caching proxy such as varnish/nginx in order to improve this, and optimize your Wordpress. (There are some caching plugins that can improve speed too)