No dynamic mobs: on, remove not used maps from loading to map-server + clean mapcache from not used maps, change virtualization from OpenVZ to KVM This is related to CPU used. All optimizations should be about BigO, link link link. You should not worry about it, because rAthena writed with C programming language, and it's really optimized because of that. Just avoid a lot of tasks inside loops. (regarding BigO) You already have swap on (at your screenshot) 1024MB. Yes, but 0.1mb or 0.2mb, just avoid it, a lot of memory used because of map-cache & mysql-server, not because of connected players.
I suggest you to do next things:
Don't damage your brain by such questions, buy normal VPS from good provider, like OVH (3.5$ for 2GB ram KVM virtualization, ssd, ddos protection, bla bla bla ( 2gb ram more then enough for 2k+ players (except woe) ). eathena / rAthena / hercules require very good CPU (3.5Ghz - 4Ghz+ in very active WoE will be good). Don't use any OpenVZ virtualization, and don't trust to people who suggest to use OpenVZ, i can totally destroy any of their arguments easly, because OVZ not for game-servers. I can provide you tons of links related to this question, but it's not needed, because a lot of providers will cry here and will trow to me shit. Just avoid any OpenVZ virtualization, and you will save a lot of nervous and resources. use SSD for your game-server, it's very well increase your game-server performance.