Why Google Play services upload nonstop 1MB/s everytime the device is connected to wi-fi?

This could be your router or something with the servers that Google Play uses. You could try upgrading your router or restarting it. It could also be caused by a certain type of malware. It could also be something going on with your internet provider.

I think you are infected with a malware that spy on your phone and upload to a comand and control server almost everything from your phone like: pictures, sms, whatsapp conversatin, facebook converstion, viber conversation etc, and to not affect your mobile data plan it starts the comunication with the server whenever you are connected to a wifi network... Im not a pro on android but I've done it before and I already know what happens behind, how it works and how it affects your phone. Do a backup but dont backup apps and after it try a factory reset. Install the list of apps u had from Play store again (Its better to backup only pictures/videos and contacts and nothing more) I hope it helps u.