Sounds like you might need to remove some apps or user data if your phone is a 64GB model. Just for clarity, are you saying that Settings > Storage is showing 55GB under the System (OS) category, or just 55GB is used overall?
For what it's worth, I have a 256GB model and am showing 15GB under System, 11GB under Apps and just under 40GB in user data (docs, images, etc).