Previously before the 15th Oct patch went live, I was only required to download once before being able to play immediately.
Now I have to download approx 20mb-ish data before I am able to play.
Occasionally there are additional updates that are between 20 and 50mb. These patches are normally for bug fixes and adjustments to the major patch update. https://forum-en.gw2archive.eu/forum/info/updates
The additional updates are added onto the primary update thread in the form of comments that include the bug fixes and changes. Each major update tends to have between 3 and 6 patches added to the major update over the course of the two weeks before the next major update. Each of these small patches usually require a small download of changed files, or at least a new Gw2.exe file that is about 22-23mb.
Is this what you are referring to? Or are you stating that you have to download 20ish MB every single time you run your game? If the latter, then you may want to:
Ensure your game is set to Run As Administrator in the shortcut’s Properties > Compatibility tab.
Ensure the ‘Read Only’ attribute is not set in the right-click > Properties for Gw2.exe, Gw2.tmp and Gw2.dat files in the installation directory.
my shortcut needed to be run as administrator