Performance issues are commonly on the side of the web host that has resource usage limits. This usually is the case in shared hosting environments. Please check with your web host if you have reached the said limit like CPU usage. Take a look at the screenshot below for example:
WordPress memory limit might also be a factor. Please contact your host to increase your allocated memory or you can try doing it yourself by adding this code in your wp-config.php
define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );
Another factor is if you have multiple editors editing the page, that could also be the cause. It's best to edit a page one user at a time.
Please do not compare backend load times with frontend as they are totally different. For frontend, please check our Performance guide at https://theme.co/apex/forum/t/customizations-performance/210. Just remember that the theme and builder's frontend output is only a fraction of your overall website frontend load speed. The most important factors like hosting speed, image optimization, etc are beyond our control.