6 MB of JSON is a lot. I mean, A LOT, especially for one user. I’m guessing some, or possibly a lot, of that data must be binary. Unless maybe you’re downloading an entire book.
Anyway, what I’m getting at is that you may want to store critical data in AsyncStorage with references to big blobs of data in FileSystem. You can save JSON (or any other string) with FileSystem.writeAsStringAsync() (FileSystem - Expo Documentation). If some of that data is indeed binary (like, say, impage base64 embedded in JSON), you can maybe serve that separately and download it directly to disk with FileSystem.downloadAsync() (FileSystem - Expo Documentation).
SQLite is an option, but I’d avoid it unless you really need the benefits of a relational database.
let queue = await FileSystem.readAsStringAsync(FileSystem.documentDirectory + `offline_queue_stored.json`);
let data = JSON.parse(queue);
console.log(`JSON Loaded: ${data.length} array elements saved inside.`);