"Information regarding the upgrade" that you see on the product page after clicking "Upgrade" states that "You can upgrade at a reduced price with a previous version or other authorized product. Please have your login details or serial number ready." So you may not receive the best special offer if you try to switch from 15 Edit to 15 Suite by using "Upgrade Now". As Vegas Pro Edit/Standard/Suite 16 is "on its way - scheduled to release at the end of August 2018", I would wait to see the upgrade offers then.