Only offering an educated guess here, not necessarily a definitive answer. When editing an image in Lightroom Classic, the edits are only in the catalog database as metadata, and if recently edited, in the Camera Raw cache for the Develop module.
When sending that image to Photoshop, the image and the current state of edits must be rasterized to pixels, as part of being converted to a Photoshop document. That process might require a little more memory, but possibly a larger amount of memory if the pixel dimensions of the image are larger or if there are many local adjustments to compile.
It might require less memory for it to be sent to Photoshop as a Smart Object, because then the rasterization is deferred.
I haven’t actually tested those, but it’s something for you to experiment with…if the amount of memory used varies with the pixel dimensions being sent, or depending on whether it’s sent as pixels or a Smart Object.
In the long run I don’t see a concern with temporary spikes in memory usage, because when I leave a Mac running for weeks between restarts, macOS seems to recover memory regularly, flushing data not recently used so that Memory Pressure does not continue climbing and can drop back down after a while.