artist:uso15are the same artist, near as I can tell.
uso15is the name on their FA and
garik29332155is the name on their Twitter, however the main name of their account on there is simply
garik, and shares a name with their Pillowfort account. It's entirely possible they consider
gariktheir main online handle, but it's hard to tell.
Derpibooru costs over $25 a day to operate - help support us financially!