That’s right. If you didn’t already, you are getting 15 GB of Google Drive storage. Google didn’t raise the quota. They actually unified the space across services they offered. So 5 GB from Drive + 10 GB from Gmail = 15 GB of storage space for data you need stored in the cloud.
This is a move users have been asking about for some time now, and Google seems to have listened. You can still buy more space, but for the average user, this means more access to their important data.
Via Gmail Blog