I've had Lightroom 2015 for some time and last year I decided to go the Creative Cloud route and get both Photoshop and Lightroom CC.
In the 'About Photoshop Lightroom CC' page (2007 - 2017), it lists this version as "2015.12 release" and "Camera Raw 9.12",
When I open the Creative Cloud version (2007 - 2018) the 'About Photoshop Lightroom Classic CC" it lists the release as 7.3.1 and Camera Raw as 10.3.
Am I able to update the 2015 .12 release to 7.3.1 and keep all my photos from the folders in the process?
Can this be done from the Adobe web site updates area?
Why not uninstall v2015.12? I assume your latest catalog is in v7.3.1 so it will no longer be compatible with the older version.
After uninstalling, re-start your computer, launch creative cloud and go to the apps tab. Then install the latest update.
When you launch LR Classic CC 7.3.1 for the first time, it should ask you if you want to upgrade your previous catalog. You should allow this. All of the work in your catalog, and all of the photos, are not changed.