1) Contact your hosting provider, our theme doesn’t affect the speed of backend and Cpanel.
2, 3) Try to disable all the third-party plugins, that do not come bundled with XStore https://xstore.helpscoutdocs.com/article/36-included-plugins , clear cache, and check how it works then.
Check how it works when a default theme is activated on your site.
Let us know the results.
