Id say no co2 is better than going back and forth. If you stopped using it, your plants are definately using less nutes.
Co2 is great if you are in a hurry, pumping out as many harvests as you can in a year, and everything else is dialed in.
If your not in a hurry, and hate having to fill your tank or make an urgent unexpexted trip to fill the tank, then forget it. If your at a constant 1500 ppm and go back to 300ppm, growth will halt, forcing you to fill your tank.