Swift 3.0 DropboxClientsManager.authorizedClient.files.download got very slow response

The Dropbox API itself doesn't offer control over the speed you get to the API, and just tries to use the maximum speed possible. There are a number of factors that can affect the speed at which you can upload files to and download files from the Dropbox servers though. This includes your connection to the Internet, how the data is routed to Dropbox, and the hardware specifications on your device.

When it comes to your Internet connection, you can only upload/download as fast as your Internet service provider (ISP) allows, and your speeds may be slower than what your ISP rates it. Sometimes resetting or retrying your connection gets you a different route and better speeds, but that is outside of our control. Some ISPs also throttle sustained connections so if you see an initial high connection speed followed by lower speeds, that could be the reason.

The specifications of your hardware can also play a part. If you own an older device, your device may not be powerful enough to upload files at a faster speed.