How to increase email piping execution speed?

To achieve this you need to use the external cron method. You have to set cron in your hosting control panel. You can set up the external cron directly to the wp-cron.php file. Please see this article for more information. This will help you to set up an external cron. After that go to Support > Settings > Email Piping > Other Settings > Cron Execution Time and set it as per your requirement.