We tested this procedure a lot over the years and can ensure that it will work for small communities using a 1GB VPS just fine. It even terminates additional Unicorn workers to reclaim memory during the upgrade to help.
You can read the code that came from this commit:
https://github.com/discourse/docker_manager/commit/2bc201509216bb9181419e0a87a5bde3866087c7
If you can reproduce it failing on a Digital Ocean droplet we are happy to take a look into it.
If that is a must you can fork the plugin and adjust to your needs.