Have you tried checking your PHP memory limit and see if increasing it makes the Pro builder load faster?
To increase it, please edit your wp-config.php file and insert these lines:
define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );
In case the issue persists, kindly provide us with your admin details in a Secure Note so that we can check your setup and provide some suggestions.