Which scenery are you using ?
Every vehicle in GSX that doesn't spawn on a parking, is correctly starting from a vehicle parking so, if the scenery you are using doesn't have a vehicle parking nearby or, even worse, doesn't even have a vehicle parking, or if the vehicle paths are not made correctly and are forcing to calculate a very long path or, even worse, if they are missing, this will affect the time the vehicle will take to arrive.
If the airport is designed realistically, with proper vehicle path in their real like positions, with proper vehicle paths connecting to the terminals, the vehicle shouldn't take much longer than in real life, since they drive at realistic speeds.
