I'm a bit late to the show but if your server has 2GB total then you shouldn't even consider running Minecraft at all since 2GB is barely enough to run the Operating System, given a 64 bit OS.
Personally, I'd opt for at least 8GB total for a server, since I'd also run it using Integrated Graphics (GPU not needed for a server) which uses 256-512MB ram off the top*, 1-2GB for the OS and you will almost always want to add something later on that will increase the memory requirements, like new mods or Server Admin tools.
In addition, 8GB can be 1 8GB, 2 4GB or 4 1GB DIMMs... 2 & 4 GB DIMMs are usually cheaper and you'll want dual channel ram for more efficient operation (needs an even number of DIMMs).
* Exception: New APUs, combination CPU/GPU dies in one chip. Ryzen APUs (with Vega GPU) use 512MB for graphics Ram up to 8GB (self allocating) in my laptop with graphics intensive applications, I've not seen much on the new Intel chip w/Vega graphics, used in the "Hades Canyon" NUC, yet but suspect a similar behavior.