Probably shouldn't judge the entire game by personal performance in one scene ( as mentioned it is one of the more challenging that exists).
I don't get the memory errors you do when I played it myself, nor when playing your saves forward in time (I've played forward hours and hours), nor did I have the surfacing sub issue - unless it just happens days later in game from when the save is - perhaps that happened due to other issues. Played on fresh game start and only bmng and borders layers on, some time ago I played that scene for about 3-4 days (real-time) straight without restarting the game without issue. Test was on 1147.16, played in editor-mode. I'm curious for how long you were playing the save before these things happened and what the meme usage was at when you ran into these things.
As BDukes mentions perhaps some the memory errors are more a system, drivers, or .net runtime issue on your end worth investigating. That said one thing you can do if you keep running into that issue, is watch command's memory usage over time for larger scenarios (3000+au) and if and when it starts getting to around > 2.7 gig sustained (not spikes), pause your game,clear the log if don't need it and it's excessive, save, and restart the game. The game can use more but around the mid to low 3's, you're likely to hit process limits, if you're getting out of memory errors below that, something else is likely wrong. One reason for a exe restart every so often is it'll clear some of the data that gets cached, some of which doesn't always get culled over time, for example it started about 1.4gig growing to 2.7 (after about 12 real hours playing doing a ton of stuff and loading up lots of tile\layer data), cleared log, saved,reloaded and it was back to 1.5gig.