I agree that we should check how loud we listen to movie soundtracks and music. However, cumulative in this case would be continuous exposure within a tight time frame, and over and over again. Film soundtracks have peaks and valleys, and there is no long-term exposure to high levels continuously within the film. You also don't get a continuous level (except with perhaps the dialog), the level is always vacillating between loud and soft, and everything in between.It bears repeating this message, if only to save someone else from destroying their hearing. 115 dB peaks in my opinion are about 10 dB too high. It’s cumulative damage. Think of it like new tires on your car. Watching a loud movie is like doing burnouts and donuts. Do enough of them and…..except you can’t just go buy new ears/hearing. Calibrate to 75 dB and save your hearing.
If I were using a jackhammer on a construction site or working on an airport tarmac, then this would constitute a danger to my hearing because of the continuous exposure to loud sound for extended periods of time. Hence why these workers use hearing protection as a requirement. These folks are exposed to sounds in access of 115-130dbs continuously. I don't really think the burnout and donuts analogy really applies to film soundtracks, but it most certainly does to live music. Live music has a continuous level coming through the PA system, and often that level is too loud.
Your last bit of advice is sage for sure.