To transfer data from one Gmail account to another, you should use
eSoftTools Gmail Backup software. I have also transferred my data to another account using this software and that too very quickly. You can also transfer data in just a few minutes using it and that too without losing any data. A free demo is also available in this software, from which you can download 20 emails from all your mail folders for free.
Read more:- Transfer data from one Gmail account to another