My wife and I both have iPhone 6s. She upgraded and has regretted it since. Very slow wake up, unlocking, and app switching are just some issues. There's a lag

My wife and I both have iPhone 6s. She upgraded and has regretted it since. Very slow wake up, unlocking, and app switching are just some issues. There's a lag with most actions. Random app crashes (even those updated), and battery life has dropped significantly.