Hello SillyGoose5,
Thanks for reaching out to the Apple Support Communities! I understand that you're looking for some information on how to optimize the storage on your iPhone 6s Plus.
To begin, you can learn more about what's contained in Other and System under the "Content categories" section of this article: How to check the storage on your iPhone, iPad, and iPod touch.
Next follow these troubleshooting steps:
1 - Using iCloud Photos is a great start. If you haven't already done so, turn on Optimize iPhone Storage for iCloud Photos. You'll find the steps under, "Save space on your device," from this article: Set up and use iCloud Photos.
2 - Create a current backup of the data on your iPhone. Having a backup of your data is like having an insurance policy, you don’t plan on using it, but it’s great to have if you need it. Here’s how to back up your iPhone: How to back up your iPhone, iPad, and iPod touch.
3 - Check for any iOS updates: Settings > General > Software Update. At this time, the latest version your iPhone 6s Plus can run is iOS 13.4.1.
4 - Update your iPhone, iPad, or iPod touch . If you're unable to update to iOS 13.4.1 due to not having enough storage, you can go to Settings > General > Reset > Erase all content and settings. This will allow you to erase all data on the iPhone. You can then set the iPhone up as new and update it to iOS 13.4.1.
5 - If you've had to erase, you'll need to then restore your backup to your iPhone. Do this by again going to Settings > General Reset > Erase all content and settings > then restore your backup to your iPhone during the Setup assistant.
6 - See if there is any change in how your iPhone performs and what happens with Storage.
All the best!
