Other than a 15cm display and a 4GB RAM, the phone will be pretty much like the rest of the mid-range Galaxy A phones.
As per the AnTuTu benchmark spotted by Sammobile, Galaxy A9 Pro will have a Full HD display, 32GB of internal storage, a 4GB RAM, a Snapdragon 652 processor with an Adreno 510 GPU, a 4,000 mAh battery, a microSD slot and a 16MP rear camera. It will have Android 6.0.1 Marshmallow OS.
We already know Galaxy A9 Snapdragon 620 (MSM8976) processors will have four Cortex A-53 CPU cores and four Cortex A-72 cores. It will also contain an Adreno 510 GPU as well. The phone was also slated to feature 32GB of internal storage. 3GB of RAM, 16MP and 5MP cameras as well as a 6-inch Super AMOLED display. So although this is similar to the Pro it is unlikely that both will have a 6-inch display. The Pro is too similar in spec and there is no need for Samsung to launch another 6-inch phone at the same time. The inferior RAM and processor suggests that Galaxy A9 won't need powerful engines to run its gigantic display.