No one needs 2GB of RAM right now on an iPhone. The only other device with 2GB is the iPad Air 2, and that's running the full suite of multi-tasking features. There are only going to be three devices (assuming both 6s phones have 2GB) out of a total 18 running iOS 9 with 2GB of RAM. Two of those devices even have 512MB of RAM (4S and iPod Touch 5th gen).
Raising the minimum storage from 16GB to 32GB is far more important than a RAM upgrade. Why? Because higher res photos, 4K video, and offline music are going to eat up storage like crazy. Purchasing additional iCloud storage or having to constantly dump content from your phone to your computer is much more of a hassle than any delays people are seeing now with 1GB or even 512 of RAM. If you're on vacation, have a bunch of offline music saved, and are snapping photos and videos, you'll run out of room. There's not much you can do; you've reached the limit of your device. You won't get that with RAM at this point.
I'd actually argue that 2GB of RAM is coming because of what is planned for iOS 10 (iPhone multi-tasking). I could see the iPhone 6S & 7 getting the full multi-tasking suite, so you'd need people with the 6s to beta test that. Then every other iPhone would get maybe picture in picture and slide over, and the 4S and iPod Touch 5th gen would either lose iOS support or not get those features.