I can see you both resize and compress. With 85 in compression I think that it is the resizing that makes the most difference. Have you tried to experiment with a larger image but more compression. 75 often works well for me and you may be able to double the resolution for the same file size and still don't have noticeable compression.
The Python scripts uploades directly to Amazon, so I don't think it will go any faster than this. In case of a broken upload, have you tried just to run the Python script again? Some people says it just resumes automatically.