Welcome to Android Central! I assume you mean a Galaxy S7, correct? From what I can find, the OS and other bloatware on that phone take up at least 8 GB of the 16 GB of total storage the phone has, so it doesn't take much else to get up to 12 GB used:
https://www.droid-life.com/2016/03/01/galaxy-s7-system-storage-install-apps-sd/. You can resolve this by either getting a new phone with at least 64 GB of internal storage (16 GB is way too little if you want to install more than a few apps), or just accept that your phone is good for only basic usage.
If you root the phone, you can remove some of that bloatware, but be careful -- if you delete something important, the phone might be irretrievably bricked.