Dropbox API to create a file, write in it via stream and then close the file.

Your connection speed to Dropbox depends on the routing you get between your ISP and our servers, and may be slower than your ISP's rated speeds.

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 chunk size you use will also affect your overall transfer rate though. Smaller chunk sizes will be more robust and less prone to fail, but will be slower overall. Larger chunk sizes will generally be faster overall, as there will be fewer calls and therefore less overhead, but you'd need to re-upload more if any one call fails.

I recommend trying an 8 MB chunk size. The optimal chunk size will depend on various factors though, so you may want to try a few different sizes. Note that you may see some improvement by only using chunk sizes of an example multiple of 4 MB. (This is just due to specifics of how the backend in implemented. There are other factors though, so that improvement may or may not be noticeable.)