Terrible performance in Map Editor, enermous map size, Map Editor bug

A few weeks ago the Map editor worked just fine on my PC. But a few days ago when I started to build new parts of the map, the map editor just went crazy. It takes 2-3 minutes at least to even load the map, lags all the time, freezes and so on. I constantly get the red "low performance" text in the right upper corner, and watch this error message 50% of the time:

Another issue is that when I open the properties of a subgrade, and OK it, the window doesn't close. It's just stuck there, and therefore I can't do anything in the editor...

It's getting absolutely impossible to build anything. And as I said before, the editor worked fine until maybe the latest patch.

My PC:

intel i5-4460 3,6GHz 4 core processor, nVidia GTX960 GPU with 4GB VRAM, 8GB RAM

According to MSI afterburner, my components are not even getting hot, so it's not like the PC wants to die. The memory is fully used, that's true (maybe I should buy another 8GB RAM to it), also the VRAM of the GPU is fully used (3,8 of the 4GB), I don't even know why. The memory usage of the editor is around 5-5,5GB.

But the processor cores are not fully used, not a single one (maybe 20-30% of the CPU time is used in the LOTUS).

Another issue occuring is the size of the map. My map is not that big, it's 8km of suburban railway and another 5-6km of tram.

That's the route of the sub. train:

So the map is not that huge, but it takes 7-8 minutes (I measured) to save and package the map. Also, often it doesn't even save the newly build parts, so I have to delete the map files and re-save again. But my bigger problem is that the map files of the map are around 3,8GB. That's ridicoulus. I have maybe 14km of mostly unbuild map, and even now it takes up 4GB. Is that normal?

How the heck should we build full cities with/without multiplayer if a single plain map takes GB-s of place? I had a bigger map in OMSI (with the same place BTW) and it only took around 1GB of place (with the objects and splines), now I have 4GB only with the map files (and another 0,5GB with the objects).

I mean this is the map at the moment, does it really look that developed to take gigabytes of place?

I use splines and tracks made by myself, but I use tie models made by Gcs7e7 (if I remember well you already told him in the past he uses too many polygons for the ties and ballasts). I remodeled them a bit, but still, a tie is around, I don't know 100 polygons maybe (the distance is default, 0,6m I guess).

Soooo, should I remodel the ties again, and regenerate the whole map because of that?

Answering Florian:

I made a few load-ups and saves to collect data:

Starting up:

loading.txt  loading2.txt

Loading tiles...etc:

tile_loading.txt

Idle:

After saving and exiting the editor:

I recorded these while having running only the Map editor, a paint and notepad (and the task manager of course).

I think I do need a bit more memory, since as you can see I don't have much left, even only with the Map editor running. And usually I have big aerial photos opened in the background (old aerial photos from the 60's which I build the map with) which use another GB of RAM (and since I usually run out of memory, another 2GB in the %Temp%)

I have 1600MHz DDR3 RAM, one piece of 8GB board. Unfortunately I cannot install higher frequency units since that's the maximum my motherboard can use.

@Edit:

So, if I want to change the ties, what do I need? Remodel them, upload in the container (Content Tool), that's clear.

But even if I just update them (same name, not new ties), do I "only" need to regenerate the tiles, or do I need something extra to do? Like opening the properties of the tracks one by one, ok-ing them, or modify the tracks...or something else? I hope I don't have to delete all of the tracks and replace them.

Well, it's kind of solved the problem. It now takes only around 1,4GB (still not that little, but better than the 4GB), I have around 10-15fps more, and now it only takes a few minutes to save. But I did have to click and OK every single track in the map, that was painful