You CAN play on 8GB, because one of my testers did.
Just don't use maps with compo pack POI's, 6k or 8k max, increase virtual memory.
My laptop is ancient (Dell Latitude E5540 or something), has 8GB of RAM and a 2GB GeForce FX graphics chip from a decade ago.
I DO run 7dtd+DF on it and it is an okay experience at 720p. I have all the eye candy down to minimum (terrain detail at lowest does the most to help). There are issues in the city areas, but overall it performs at the 20-30 fps range. Playable, but not pretty.
Smaller maps 8k and under perform reasonably. There are stutters here and there as things load up or spawn in.
I reboot before running 7dtd, and keep my background apps minimal.
****I also reboot the machine if weird issues start to appear in game (I play single player mostly, so not an issue for me to do so). I would call it mostly stable, unless I ignore symptoms of a problem (like very long delays in placing or upgrading blocks or invisible blocks).
My desktop has 16GB of RAM, and also uses integrated graphics. I would consider it far more 'stable' running 7dtd than on the 8GB laptop (smoother, less stuttering for certain; longer sessions between issues).
Summary: running with 16GB is more stable than 8GB (smoother experience), but you CAN run it with just 8GB (with caveats).
Recommendation: if you can affordably upgrade your machine to 16GB, do so, it may help in other ways too.