If you were happy when Google announced 10 GB of storage for you, it’s time for you to be happier because Google just announced that the storage capacity of Gmail has been increased to 15 GB. However, there’s a catch.
Up until now, you were allowed 10 GB of storage on your Gmail and another 5 GB for your Google Drive and Google+ photos (if you choose to store full resolution.*). But when the change rolls out to your account, you will have a total of 15 GB of storage shared across all of your Google services.
This is definitely a good thing. If you use a lot of attachments and your Gmail storage is nearly full, you would now be able to take advantage of the extra 5 GB storage. On the other hand, if your email is nearly empty, you get almost 15 GB for your Google Drive or storing full resolution photos on Google+.
In a nutshell, Google just allowed you to take advantage of your total 15 GB on any of its service you want. The actual capacity hasn’t really increased. You already had 15 GB in total. Google just merged the maximum free capacity a Google account can have and let user “have it their way!”
The changes haven’t been applied to all accounts, but Google said it is in the process of rolling out.