I was going to suggest copying the file.
This is the advice I gave MikeMax for a similar read issue:
The first time you read the file, it is in the apk itself and needs to be extracted. If you do an initial read and then store it back to the same path, it will be put in the app sandbox area and probably read much faster after that.
Since this would be a one time process, check for a small file of any name that doesn't exist until the app is run. If the file does not exist, put up a message saying that a one time initialisation is being done. Then read the file and write it back and create the small file (only needs to be a single value) and it will be found the next time the app is run.
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master