I'm using my Spotify app on my iPhone 6S+, and I've been having this problem for some time now.
I have quite a bit of music downloaded onto my device, as I travel for work and like to listen to music as I fly--as any reasonable person would. However, whenever I open the Spotify app, it takes a good 45 seconds to "initialize" (or something) before I am able to do anything. Moreover, the app will occasionally freeze and crash suddenly.
I have tried updating my iPhone as well as the Spotify app. I've totally uninstalled and reinstalled the app, and redownloaded all my music--but to no avail. I continually have to force close the app and repoen it. Nobody like waiting 45 seconds for the app to open, after which suddenly crash.