Minecraft Server RAM leak?

Hi, I am running a server with a dedicated host, on 6GB of RAM. While we are not experiencing any lag, whenever I type /lag, our free memory is very low. Even with the small amount of chunks loaded. I am wondering if it is a plugin problem. Below is a list of the /lag info and a list of plugins; nocheatplus and ontime are both using a MYSQL database.
04.05 22:05:37 [Server] INFO The End "world_the_end": 0 chunks, 0 entities, 0 tiles.
04.05 22:05:37 [Server] INFO Nether "world_nether": 0 chunks, 0 entities, 0 tiles.
04.05 22:05:37 [Server] INFO World "world": 2,289 chunks, 759 entities, 648 tiles.
04.05 22:05:37 [Server] INFO Free memory: 950 MB.
04.05 22:05:37 [Server] INFO Allocated memory: 6,077 MB.
04.05 22:05:37 [Server] INFO Maximum memory: 6,077 MB.
04.05 22:05:37 [Server] INFO Current TPS = 20
04.05 22:05:37 [Server] INFO Uptime: 8 hours 33 minutes 50 seconds

Plugins (29): TimTheEnchanter, WorldBorder, MultiWorld, WorldEdit, MassiveCore, ColoredSigns, Vault, PermissionsEx, CombatTag, DestroyBedrock, WorldGuard, SilkSpawners, ChestShop, ClearLag, Votifier, HolographicDisplays, mcMMO, Essentials, EssentialsProtect, EssentialsSpawn, RegionForSale, VoteLink, EssentialsAntiBuild, OnTime, CompatNoCheatPlus, EssentialsChat, Factions, FactionChat, NoCheatPlus