Worth remembering that CPU is throttled to battery health over time, so you’d want to compare your 6 as it was on day one. Not to say that your new phone isn’t

Worth remembering that CPU is throttled to battery health over time, so you’d want to compare your 6 as it was on day one. Not to say that your new phone isn’t faster, but your Spotify example is exactly my experience just getting a new battery for my iPhone 6 two months ago.