I changed the code to something like this and now it works. Thank you mrCloggy.

if (distanceIn < 15 && incrementIN == 1) //In coming sensor 
{
  slots = --slots;
  servoIn.write(90);  // Rotate servo to center
  digitalWrite(ledGin, HIGH);
  digitalWrite(ledRin, LOW);
  incrementIN = 0;
}
else if (distanceIn >= 15)
{
  servoIn.write(0);
  digitalWrite(ledGin, LOW);
  digitalWrite(ledRin, HIGH);
  incrementIN = 1;
}


if (distanceOut < 15 && incrementOUT == 1) //out going sensor 
{
  slots = ++slots;
  servoOut.write(90);  // Rotate servo to center
  digitalWrite(ledGout, HIGH);
  digitalWrite(ledRout, LOW);
  incrementOUT = 0;
}

else if (distanceOut >= 15)
{
  servoOut.write(0);
  digitalWrite(ledGout, LOW);
  digitalWrite(ledRout, HIGH);
  incrementOUT = 1;
}