Multiplayer world crashing "description: watching server" caused by Out of Memory

I've been testing a copy of my 1.12.2 world in the prerelease and while its been laggy and run out of memory a couple of times, now I have a situation where

1. I login and cannot interact with anything

2. The client is booted with 'Timed Out'

3. The server crashes shortly afterward.

I've repeated this several times and had the same results. I've increased the memory available to 4G and had the same result.

[16:10:51] [Server thread/INFO]: Preparing spawn area: 96%
[16:10:51] [Server thread/INFO]: Preparing spawn area: 100%
[16:10:51] [Server thread/INFO]: Time elapsed: 1416 ms
[16:10:51] [Server thread/INFO]: Done (2.346s)! For help, type "help"
[16:11:18] [User Authenticator #1/INFO]: UUID of player aeduna is e96c9253-be4d-44cb-8981-60eda991a208
[16:11:19] [Server thread/INFO]: aeduna[/192.168.1.200:36008] logged in with entity id 176 at (1024.77793444543, 97.9931355636394, -2062.776598736978)
[16:11:19] [Server thread/INFO]: aeduna joined the game
[16:12:19] [Server Watchdog/FATAL]: A single server tick took 60.00 seconds (should be max 0.05)
[16:12:19] [Server Watchdog/FATAL]: Considering it to be crashed, server will forcibly shutdown.
[16:12:20] [Server Watchdog/ERROR]: This crash report has been saved to: /home/minecraft/preniu/./crash-reports/crash-2018-06-06_16.12.20-server.txt
[16:12:20] [Server Shutdown Thread/INFO]: Stopping server
[16:12:20] [Server Shutdown Thread/INFO]: Saving players

Memory: 3049217984 bytes (2907 MB) / 4194304000 bytes (4000 MB) up to 4194304000 bytes (4000 MB)