As for the iPad Pro, there was little doubt, but now it seems that the amount of RAM that comes with iPhones 6s / 6s Plus:
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/X8Ym4DtamS
– Hamza Sood (@hamzasood) September 13, 2015
According to codes found in Xcode by the hacker Hamza Sood, the new iPhones even have 2GB of RAM, while the iPad Pro goes to 4GB.
The new A9 (X) chips alone should already provide optimum performance gains for the new devices, but adding that to double the memory we can expect an even better experience and with more apps running simultaneously. In the case of the iPad, this is even more valuable considering the new "Split View".
Recently, Sood had also confirmed that the new iPhones would come with Force Touch technology which, as we know, is now called “3D Touch”.