iPhone 6s Storage vs. Galaxy S6 Storage
The Galaxy S6 doesn't come with a microSD card slot, a product of its iPhone 6-like design. To compensate, Samsung's offering the device in three sizes including 32GB, 64GB and 128GB. That's actually better than what Apple offers with the iPhone 6.
The iPhone 6s could mirror the iPhone 6 with a 16GB/64GB/128GB lineup. A report from the credible 9to5Mac shows an internal part that hints at a 16GB base model for the iPhone 6s. It doesn't confirm it but it leaves the door open.
Another report from The Korea Times claims that Apple is negotiating with Samsung to boost the internal storage of the iPhone though it's unclear if the company will get the deal done in time for the iPhone 6s' production.