It's a widespread problem with JoomShaper template it seems. If you run a Page Speed test on their demo of your template, as well as most JoomShaper templates, you will find that they do really poorly, mostly due to images.
I brought up the issue last week but they are quietly ignoring it.
Thank you genegun, but I want to talk about the time that is too long between image changes, I would like to reduce this time and there are no options.
Thank you