The speed of the website is depending on many many factors and having the latest version of the theme is just a tiny percentage of the possible reasons.
Actually, there are professionals that are focusing on speed checking many aspects from the amount of the media to the server performance.
We as the theme support are not the ones to be able to help you on this matter. You can start your research here if you are interested in doing the checks yourself.
But we are recommending that you seek a help from a professional regarding this matter as they will use some tools to check and give you proper solutions.
Our theme is one of the most performant themes in the business and you can check that by testing the speed there.