Can I use Rescuezilla to move my Zorin 15.2 64bit to the latest Zorin lite version so i can retain all my saved data ?
I'm afraid Rescuezilla*** can't do for you what you ask. Even if it could I wouldn't suggest it. When making a big jump in versions such as 15.2 to 18.1, upgrading is not a good idea for insuring data integrity and maintaining system stability. It becomes a positively bad idea when you add switching from core/gnome to lite/XFCE.
Much better to make a list of your programs*, back up your data**, do a clean install of the new os on your machine, update that os as it requests until finished. Then reinstall your programs and copy over your data.
Detail:
*Make a list of every app you installed that didn't come standard with the OS. If you aren't sure which are which, write them all down. This will help you remember what to reinstall once the new system is in place.
**Backup your data by going into your file manager and doing a manual folder to folder/file to file copy to a second usb flash drive (not the one with your new os on it) . Go to /home/[your-username] and copy and paste the contents of folders such as Desktop, Downloads, Documents, Pictures, Music, Videos, Templates, etc. etc. into similarly named folders (make the names slightly different, such as Desktop1, Downloads1, Documents1, etc.) on the flash drive plus all text files that exist in the /home/[your-username]. After your new install and updates, reverse this process to copy the data over to the new machine. Plug in the data usb, go to your file manager, open up Desktop1, copy the contents, and paste that into Desktop on the new machine. Etc. This is easiest if you open two copies of the file manager side by side.
*** (It isn't a bad idea to make a full image of your entire 15.2 system for insurance and for this you can use Rescuezilla. (But that image won't be accessible for copying data, etc. It's a single compressed image for an all or nothing restore of your 15.2 system in its entirety. )
You could also create a separate partition on the hard drive just for your data and copy your personal files there, as described by wsmather. However, this might make the installation of Zorin 18 a bit more difficult, since you would likely have to use manual partitioning during the installation if you plan to make a fresh install of the OS.
Saving your datas to an external drive or USB flash drive before the installation is easier. You can also create a separate data partition afterwards, if you like.
If you have very old hardware that’s more than 10-12 years old and perhaps have an NVIDIA graphics card, it’s worth considering installing “just” Zorin 17 Lite for now and using it as long as it’s still supported. It will likely run better than the current Zorin 18 version. You could upgrade next year with the upgrader tool to Zorin 18 Lite.