If you’re using multi-site install, my understanding is that the number of sites barely matters, what counts is the number of simultaneously active users on all sites.
If you are simply asking if you can downgrade your dev instance, the answer is yes. You likely will never have enough active traffic to warrant the same setup you have for your active production sites.
For comparison purposes, my sandbox/dev site is a 1 core 1 GB RAM box on a 25 GB SSD and when I’m using it, it doesn’t feel sluggish to me at all. Rebuilds can take 15-30 minutes (since it is a full-fledge docker setup – not sure if you used the dev setup or official docker setup, but I imagine it will work with those specs for either).