Hi there,
Container size will change depending on the device where it’s being viewed. In my view, your home page’s parallax container has 1900×999 size. Hence, you can try 1500×789, just make sure to increase the canvas and put design elements within 1500×789 in the center.
You can check the size of the container by using browser developer tool’s inspector. Inspect the section and you’ll see its size.
Thanks.