Yes it is only 4 simulator sessions, but leading up to the simulators you have done 13 sessions in a flight training device doing normal flights, two engine instrument approaches. So by the time you get to the sims you should be relatively proficient at doing normal procedures and pushing off the gate within 15minutes.

The only thing the sims add are engine failures. You do everything else in a FTD because it's cheaper. And because the FAA only allows type rides in a simulator. If spirit could give type rides in an FTD to save money they would.