The battery was very bad on my iPhone 6S Plus and the recent iOS update made the phone slower for me.
The repair was very easy since the repair guide was excellent. Organization while doing the repair was of utmost importance so I made sure I wrote down my steps and marked the screws properly. Overall it was very easy than I initially thought. Everything works perfectly fine and my phone is as good as new again.
1. The organization is the key.
2. Have lots of lights are the screws are very very small.
3. Read all the comments on every step before doing anything else. Also watch the youtube video guide at least once.