Check wifi settings if you are not using proxies on the phone. It may discrease your speed sometimes.
Maybe it sounds silly but try to test your internet speed by other app.
I had the same problem 1 year ago. As @Pugs1957 said, try connect USB keyboard with Micro USB to USB adapter. It costs a few $. This method worked for me.
Yes.
1) Download and unpack this zip https://1drv.ms/u/s!AmsccWi-ldMei3UMlW9rjZwWoDQs
2) Download stock firmware from here Firmwares - SamMobile and extract it from zip
-- choose your phone model and select firmware from the list (btw, u need to be registered to download it and download...