Firstly, the extra space is for two years. Secondly, I think by then, we would get extra space, so I would be having more or less 25GB of space. If not, then I shall go down the 15GB.
About the quality, these are basically for sharing with my family members - videos + pics - G+, since I prefer that over FB. I also plan to dumping a full size backup to flickr - where the space is a whopping 1TB.