It will also depend on how many times it was repainted over the years. My house was built in 1978 and had no extra paint in most rooms, one coat in a couple of others. It was a tedious job, but it is all off.
We sprayed it lightly, let it soak, then scraped off what came off easily. Then a wet sponge tool off the rest. In my case, the ceiling under the popcorn we in very good shape so it was just a coat of primer, then ceiling paint. In a few areas, it came off dry, but th at was the exception. Ed