How to free as much RAM as possible?

Hey! I have an iPhone 6 that has 1GB of RAM. I recently installed an app to check my memory availability and I only had 3% (around 30MB) of ram available. I tried using the app's booster, also did the Hold power button and home button trick (That resets the RAM) & I reset the phone also. My free RAM was still at the mere 15% (around 150MB). This was and still is annoying me because not having free RAM has made my phone really slow. I also stopped other stuff in settings like Auto-Brightness and Background app refresh yet that didn't help either. I actually deleted some apps too to see if that would help. None of that helped either. If anyone could tell me a way to free RAM on my iPhone or knows a software that could free RAM (I have a Windows computer) Please tell me! Thanks!