Hi, this is not Apple Support. Apple and Apple Support do not participate here. Everyone posting and commenting are fellow Apple users, just like you.
So, with that said, no one here is trying slow your device down. Please be specific in what your want assistance with. If that is inconvenient, please contact Apple support for further assistance.
You’ll need to have Apple perform diagnostics on your iPhone. It can be done in person at an Apple Retail Store or at an Apple Authorized Service Provider. You can also contact Apple Support and request remote diagnostics.
If you’re in the US please call 1-800-MY-APPLE or outside the US, consult the support articles below. In Canada call 1-800-263-3394
Contact Apple for support and service - Apple Support
Genius Bar Reservation and Apple Support Options - Apple
Explore Service Locations
Official Apple Support