Been using the 4S for a couple of hours now and still no "update" to beta 3.
As we speak I'm restoring my 5S's backup onto my 4S and will start using it as my daily driver for a couple of days (or weeks) now to figure out whether a) a 3.5" screen is still usable in the age of the 5.5" mid-range phone (which I'm unsure of), b) a four year old phone is still fast enough for what I need (which I highly suspect), and c) the battery still holds enough charge to get me through the day (which I highly doubt). After all I do plan to take this phone on my year-long trip and need to figure out where exactly on the dream-realism continuum that thought resides or whether I should rather get a cheap Android phone for that year.
So far, iOS 9 has been a blast on the 4S. Much faster than iOS 8 although I must admit I haven't been using it much.