Regarding the Speed of the site, I have checked your site speed and here are the results: https://gtmetrix.com/reports/clubjerseys.online/3WofIdPY/ as you can see in the tested URL, the things that need to optimize in order to boost your site performance. The thing is our theme is already well-optimized all of our demos content is optimized. But, whenever a customer changes the demo content with his/her content and if the content is not optimized then he/she must need to optimize the content in order to get better performance results. Now, to optimize the site content to speed up the site load time you can use the WP Rocket plugin on your site. It will help you. Here is a link to documentation about the WP Rocket and how to use it: https://xstore.helpscoutdocs.com/article/128-how-to-improve-wp-rocket-settings-with-xstore
