The new chip will be 32nm - as for faster a9 or a15, I'm hoping a15, but I think apple will use whichever solution will use less power.
Quad a9 is as fast as dual a15...anyone's guess...
Not really. For the vast vast majority of applications, dual a15 will be much faster.
Hopefully A9 or A15, as the current CPU is getting a bit long in the tooth. A5 processor is in the 4 / 4S. The iPad 3 was the first of the new A5X CPU. I think they should go for a quad core A9 processor - the same one used in the PS Vita which is a quad-core CPU / GPU in one.
They won't use the same one in the Vita. That has a special SiP SoC with the VRAM mounted directly on top of the SoC for a 1024 bit wide memory interface to the GPU. Apple doesn't need anything that exotic.
The A5 debuted in the 4S. The iPhone 4 carries the A4 processor. So, in that regard, the A5 is only less than a year old. To my mind, power consumption and heat are the two main issues. My 4S runs smooth as silk even running graphically intensive games. I can't see the need for much more but longer battery life and less heat could come in handy.
A5 debuted in iPad 2. At the time of this iPhone's launch, it will be 1.5 years old.