If your Visual Composer loading slowly this will be helpful to you to solve the issue, open your wp-config.php file. (You can find it at the root directory of your WordPress installation) using a text editor.
Now, paste the following codes:
define( 'AUTOSAVE_INTERVAL', 180 ); // Seconds
Just above of the /* That’s all, stop editing! Happy blogging. */ line.
If 180 not resolves, then add 240, 360 etc & check.
Hope this helps you