As an extreme shorthand I can see why you’d say this, but don’t you agree that the go/nogo for running Discourse is RAM+swap? 1+3 is just as good as 2+2 from a point of view of go/nogo.
It’s only performance (responsiveness) which cares how much RAM you have.
RAM+swap is the right thing to check and test. Memory=RAM+swap.
BTW if something is not working with no obvious evidence as to why, and especially if you suspect memory shortage, it’s worth checking for the out-of-memory killer, also known as the OOM-killer. I recommend
dmesg|egrep -i "memory|oom|kill"
Edit: for convenience I’ll add that to my list of standard instant diagnostics:
cat /etc/lsb-release
uptime
df -h /
free
vmstat 5 5
dmesg|egrep -i "memory|oom|kill"
ps auxrc