Of course the most obvious source is what i overlooked as a possible source of the lag.

Congrats! your map got featured in the official news post as one of the favourites of the comp.
I especially love how you used the lights on/lights off mesh to make the freight wagons loaded/unloaded, that was a great idea.
If you want the map to load faster, i recommend simplifying down the track mesh model, since it's quite high-poly