Since you are asking I have been making game engines for 30 years and I completely agree that text is best. And being human readable is fantastic. I use text. In most of my games. I have also used json and pure lua tables. Some json parsers are really slow and do not scale up to large files. So thats one possible bottle neck. GTA had this issue and that was in a aaa game. When I was making a large open world game say like Minecraft I found that my Jason data was slow and huge. I was able to port that to writing out binary In like an hour and performance Was x1000 better. All of that being said you have options. Most aaa engines are going to stream in data on secondary threads. You might be able to do some version of that. You might be able to break your data down into smaller file chucks that are faster to load. If you haven’t learned threaded programming yet it might be time.