sudo systemctl stop virtualgps <--- This stops a running virtualgps service
sudo systemctl disable virtualgps <--- This prevents the virtualgps service from starting at boot time, but it doesn't stop an already running virtualgps service.
In case you have problems getting a fix from your GPS, then it's a good idea to put your usual home location into /etc/location.conf
That way, if you can't get a fix, then you can start the virtualgps service and use it with GPSD as normal.
To start:
sudo systemctl start virtualgps
You don't need to enable virtualgps in order to start it, that just makes it start automatically at boot time.