I changed themes from VOUX to GP and my site speed slowed down tremendously. The first section of my home page loads way after the bottom more static page loads. I also got an error that all my images are missing width and height attribute and I think this is somewhat slowing down my homepage. There of course, could be another reason why this is happening.
your home page is built using Visual Composer and for some reason it looks like it is requesting every single featured image you have on your site – around 700 in total. So the page is taken a huge amount of time to load.
If you visit a single post or an archive page, which is GP, then you will see it loading in a more respectable time. To improve their speed i would look at reducing the number of related posts on your single post and the number of posts displayed on the archives.