As Adobe Photoshop Elements 15 was released in 2016 it was only tested and confirmed to run on the newly-released (at that time) macOS 10.12, and the two previous versions of macOS, 10.10 and 10.11.
macOS 10.14 was still a few years off, being released in 2018. Hence, Photoshop Elements 15 was never "officially" tested on macOS 10.14.
So no "official" guarantees, but you shouldn't have any problems - there have been plenty of users on this Support Community who have been running Photoshop Elements 15 successfully on their Macs running macOS 10.14. Only common problem I could find is outlined in this Adobe Knowledge Base article (it's for Photoshop Elements 2019, but still applicable for Photoshop Elements 15 too):