Artesan0, could you check your current installation in terminal with
zorin-appearance --version
See what kind of response it gives you.
Not sure about this, do you mean the update 15.3 including the latest kernel?
You might try removing and reinstalling the following packages in terminal.
If you are using Zorin Core:
sudo apt-get install zorin-appearance
sudo apt-get install zorin-appearance-layouts-shell-core
sudo apt-get install zorin-appearance-layouts-support
sudo apt-get install zorin-auto-theme
If you are using Zorin Lite:
sudo apt-get install zorin-appearance
sudo apt-get install zorin-appearance-layouts-xfce-core
sudo apt-get install zorin-appearance-layouts-support
sudo apt-get install zorin-auto-theme

