Yes, a user can change from Lite to Core.
sudo apt install zorin-os-desktop
This is also true for users switching from Core to Lite:
sudo apt install zoirn-os-lite-desktop
In your case, you would need the Pro included Premium Packages and I cannot recall all the package names needed off-hand. I do not want to mislead you by giving you the wrong info- But the ZorinGroup can help you get Pro Core set up without a reinstall.
As above, our goal is to get you the Pro Desktop you chose at checkout.
The reason Fractional Scaling is tricky:
Imagine you have an odd number like 3pixels. At 1.5 scaling, you end up with a line 4.5pixels in size. Which... is not possible. It needs to be whole numbers.
To patch this, anti-aliasing is used. So, you can see the problem there.
Fractional scaling on GNOME uses oversampling, which means rendering at a higher resolution, then scaling down with integer scaling resulting in higher CPU and RAM usage.
Not a lot though and if you have a good processor and RAM, you probably won't notice it.
Back to your Immediate issue until you can switch to the Pro D.E.:
XFCE4 supports DPI and now, HiDPI scaling.
https://wiki.archlinux.org/title/HiDPI#Xfce
You can see there are a few steps involved, but by setting scale to 2, then using an environment variable of GDK_DPI_SCALE=0.5, you can force fit the appearance of 1.5