Is 1.4GB of RAM enough?

I am running a Minecraft server, and I have allocated 1.4GB of RAM to it (I’m running it on an old laptop with 2.4GB of RAM). The server seems to run fine with 3 or 4 players on it at the same time, but have yet to test it with more players (I set the player limit at 20 players). The server is completely vanilla (no mods or plugins). I am running the latest version of the MineOS distro.