Currently, my LibGDX game consists of a 512 x 512 map of Tiles and entities such as players and monsters. I am wondering how to efficiently save and load the data of my levels. At the moment I am using JSON serialization for each class I want to save. I implement the Json.Serializable interface for all of these classes and write only the variables that are necessary.

So my map consists of 512 x 512 tiles, that's 260,000 tiles. Each tile on the map consists of a Tile object, which points to some final Tile object like a GRASS_TILE or a STONE_TILE. When I serialize each level tile, the final Tile that it points to is re-serialized over and over again, so if I have 100 Tiles all pointing to GRASS_TILE, the data of GRASS_TILE is written 100 times over. When I go to load/deserialize my objects, 100 GrassTile objects are created, but they are each their own object. They no longer point to the final tile object. I feel like this reading/writing files very slow.

If I were to abandon JSON serialization, to my knowledge my next best option would be saving the level data to a sql database. Unless there is a way to speed up serializing/deserializing 260,000 tiles I may have to do this. Is this a good idea? Could I really write that many tiles to the database efficiently?

To sum all this up, I am trying to save my levels using JSON serialization, but it is VERY slow. What other options do I have for saving the data of so many tiles.

I also must note that the JSON serialization is not slow on a PC, it is only VERY slow on a mobile device. Since file writing/reading is so slow on mobile devices, what can I do?