Preview at WWDC likely in June, followed by September launch.
Xcode Confirms 2GB of RAM in iPhone 6s and 6s Plus, 4GB of RAM in iPad Pro
Not much of a surprise but Xcode confirms 2GB of RAM for the 6s (and 6s plus), and 4GB for the iPad Pro pic.twitter.com/X8Ym4DtamS— Hamza Sood (@hamzasood) September 13, 2015
The image asset is chosen based on the memoryClass key in the simdevicetype’s capabilities.plist. 0 = <1GB, 1 = 1GB, 2 = 2GB, 3 = 4GB.— Hamza Sood (@hamzasood) September 13, 2015
As usual, Apple itself did not mention how much RAM the iPhone 6s, iPhone 6s Plus or iPad Pro have during its "Hey Siri" media event, nor does it include RAM on the tech spec pages for any of the devices.