Freezing up and super slow

I’ve just installed Page Builder and watched the intro video. I started to create a new page and inserted an image. This took forever to complete, then the page just turns all gray and is frozen with no buttons active. I reloaded the page, couldn’t see the image I inserted but I thought I would work on my text so I created an element and put in my text. Again, when I hit “save”, the entire screen goes gray and freezes. Sometimes, my browser autosave works so at this point, I go and check the page and that text is there, no image. Have spent the past 10 minutes just getting a bit a text in, super slow to save it and it also didn’t save the page setup where I set it to only have one column in my theme since I don’t want the sidebar. My theme is “Mantra” by Cryout Creations. I’m using the latest version of Chrome on an iMac with 16gb Ram that has been very fast until I installed this plugin. Is it the theme? Is it the browser? I want to be able to create these simple pages, just one image and a few lines of text, in a few minutes, not 30 or so and having to do each tweak in a separate function while waiting for it to save and then go back in.