Going the IPSW route can take longer to update than using the newer OTA (over the air) method, the reason being that OTA uses smaller delta updates than the larger IPSW files, which are the full sized downloads and are often literally 10x the download size.
You can also click on “Restore” and select an IPSW instead but you will lose the existing files and settings on your i OS device.
If you have decided you’d like to update an i Phone or i Pad to i OS 9, you can install i OS 9.0.1 manually using firmware and i Tunes.
The manual firmware method is more advanced, making it perhaps best for specific reasons, like to resolve the frustratingly unresponsive “Slide to Upgrade” screen, to fix the Software Update Failed error, due to storage space limitations on the target device, because sometimes it’s just easier due to bandwidth constraints, or because you’re updating multiple of the same devices.
The i OS 10.3.2 update is only a small update if you’re coming directly from the previous version of i OS 10 (i OS 10.3.1).