Hey, so I have tried to install this game today, through Galaxy 2.0.35. An error occurred, "Installation failed (E2)". Well, nevermind, I tried uninstalling it, resulting in "Uninstall failed (E15)". After that, the app stopped associating the game folder with the game and gave me the option to install it once more. However, the game folder is still there with full 13gb of data.

I use "Manage installation > Import folder" to connect them once again, the game can be launched and played alright, but attempts to unistall still result in E15.

There is no "uninstall.exe" or whatever in the game folder, third party uninstallers don't see the game.

Any ideas how to get rid of the it?

Try deleting it from Windows: Start > Settings > Apps. If the game isn't listed there either, then you can probably just delete the folder directly.