While I imagine it probably won't make a difference, could you try it going the other way? Download rather than upload. Doesn't need to be a huge file, 40-50kb should do the trick... maybe just try and download https://www.espruino.com/press/logo_square_blur.png ?
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
While I imagine it probably won't make a difference, could you try it going the other way? Download rather than upload. Doesn't need to be a huge file, 40-50kb should do the trick... maybe just try and download https://www.espruino.com/press/logo_square_blur.png ?