If you use Snap to install Spotify:
snap install spotify
Spotify startup time on my machine is ~30s.
On the other hand installing it from .deb file:
curl -sS https://download.spotify.com/debian/pubkey_0D811D58.gpg | sudo apt-key add -
echo "deb http://repository.spotify.com stable non-free" | sudo tee /etc/apt/sources.list.d/spotify.list
sudo apt-get update && sudo apt-get install spotify-client
Leads to instant startup time!
You need to change a shortcut located at /usr/share/applications/spotify.desktop. Change the following line:
Exec=spotify %U
to
Exec=spotify --force-device-scale-factor=2.0 %U