15GB is not really very much in when lots of phones can now record 4K video. I've got a 6 minute video recorded at my mothers 70th which is almost 1GB in of itself. And Google have been pushing Google Photos as a way to 'free up space' on your device by uploading everything to Google and then deleting them from your phone.
Its not really clear from what Google have announced are the going to continue offering the option to store at 'High quality' so you can store more in the 15GB or will that option be ending so they can then force you to pay for Google one?