Suggestion on copying data from server database to android device sqlite

I'm developing an Android app for salesman, so they can use their device to save their order. Currently, I can get the data by sending a request to php file, and like common practice we insert those data into sqlite in the Android so it can work offline. However, with current approach the device needs 6-8 seconds on getting the data and inserting those data to sqlite. As the data grow bigger I think it would make it slower.

I've been thinking about dumping all data that is needed by the salesman into a sqlite file, so I could only send that file which is more efficient, I guess. Can you please lead me on how to do that? Or is there any more efficient approach for this issue?

Note: Server DB: Mysql Server: PHP