I have more RAM than you, but the forum is otherwise small and this is my memory consumption:
root@elio ~ # free -m
total used free shared buffers cached
Mem: 2000 1972 28 266 38 574
-/+ buffers/cache: 1358 641
Swap: 2047 80 1967
Looks like the memory requirements of Discourse are growing somehow - I had to enable swap even on 2GB RAM.