Yeah, I found a solution and will post it here.
The only thing to do would be to update the xpad driver (from here: https://github.com/paroj/xpad)
However this failed because of missing linux headers.
Which I found, downloaded and installed from this site: https://www.niksula.hut.fi/~mhiienka/Rpi/linux-headers-rpi/
With installed linux headers, I could update the xpad driver without any problems. After a reboot, retropie and the xbox one controller 2015 finally worked together. All was well…
In my specific case (I’m using a Raspberry Pi 1B, and Linux 4.1.7+ which I obtained by running “sudo rpi-update”) the steps would be as follows:
wget https://www.niksula.hut.fi/~mhiienka/Rpi/linux-headers-rpi/linux-headers-4.1.7%2B_4.1.7%2B-2_armhf.deb
sudo dpkg -i linux-headers-4.1.7%2B_4.1.7%2B-2_armhf.deb
sudo git clone https://github.com/paroj/xpad.git /usr/src/xpad-0.4
sudo dkms install -m xpad -v 0.4
sudo reboot
