I take that back. I took one more look this morning:
You have many tilesources with massive tiles: layer01_01.tilesource has 6 tiles, each being 985*1130 and mostly consisting of transparent pixels. This tilesource alone eats a ton of memory: 985*1130*6*4 = 24Mb and you have several with a similar size. Some of them seem to consist of low resolution images of what looks like trees or something that have been scaled to fit the tilesize of 985x1130.
You should reconsider this design as those tilesources will use a lot of memory when loaded. The ground pieces could still be kept in a tilesource perhaps, but you should in that case get rid of all the transparent pixels above each ground piece. The trees could perhaps be stored in a normal atlas in a much lower resolution and then scaled to the appropriate size instead of having them pre-scaled.