Although @Philipp makes a good point, I don't fully agree with his assertions.
Now this rally depends on what you intend to do, but databases are good at efficiently persisting data and work through huge volume of data efficiently.
There are three levels of data access you need to consider. First you have your objects fully formed in memory. This generally quick access, but if you need to look through large swaths of objects to find something you need to implement the appropriate access algorithms (e.g. indexing).
In memory databases can make life a bit easier when the amount of data you handle surpasses your ability to organize efficiently. You can to it yourself, but if you are juggling a few GB of data, you are effectively re-implementing a database, just use an existing one.
Disk backed databases should be used when your data surpasses the RAM capacity or need long term storage. Databases generally are good at keeping the relevant bits in memory and hot; but yes if you get a cache miss, it will hurt bigtime. But if you use your database mostly for write only storage, they can be quite efficient. The key feature is that the write will be quick to memory and the database backend will later persist it when time allows.
Although you are not entirely clear on the details, you can have the best of both worlds. Why not keep your current game state in objects and each move / tick you write the game state changes to the database before updating to the next.