As a headphone user I find nothing more annoying than computer asking me every single freaking time what exactly did I plug in. While Windows drivers for Dell XPS 15 audio do allow you to select default, one is not so lucky under Linux.
However, Linux being configurable to a fault does offer a workaround.
You can append the following options to the end of
/etc/modprobe.d/alsa-base.conf, followed by a reboot:
options snd-hda-intel model=headset-mic
This will lie a bit to sound driver and stop the darn questions.
PS: You can also use this one liner:
echo "options snd-hda-intel model=headset-mic" | sudo tee -a /etc/modprobe.d/alsa-base.conf