A phone that wont charge could be caused by multiple things:
- A defective battery. The iPhone 6S is well know to suffer from battery issues, perhaps your 6S Plus has a similar problem.
- A defective charge port. While you replaced it, these small parts are notorious for poor quality and you may have gotten a bad one.
- Debris or oil residues inside the port (you cleaned it with IPA already).
- Defective Lightning cables and charging bricks. Always use genuine Apple cables and bricks when troubleshooting problems.
- Finally, a defective charge circuit on the logic board. This could be caused by water damage, impacts, poor quality (i.e. the cheap stuff) Lightning cables and charging bricks, especially the "automotive" ones.
The first 4 you can troubleshoot yourself and the last one requires a micro-soldering repair (not DIY).