First of all, reduce the size of the page. For example, home page size is 7.32MB, very big. Optimize images to reduce the size of the pages. We would recommend TinyPNG service, it will help you to optimize images up to 70%.
Also, install cache plugin (W3 total cache or WPRoket or any other that you prefer).
If you want you can provide us with Dashboard credentials and we’ll help you with base cache plugin setting.