Last week, my 2yo iPhone6s log-in/loading time was bad (longer than 2mins), but it's back to my typical 20-25s, and I am not updating to iOS11 until I have to.
As long as my device logs in to CC, I'm good! I guess it depends on your tolerance...
But,
anything longer than a min is too long and Deca is tirelessly working to reduce load times as their #1 priority at the moment.
iPhones older than 6s will probably be getting worse and worse as far as loading times go... blame it on planned obsolescence