Says who? That's a very dubious claim that movies are 'meant' to be listened to 15 dB louder than music.
For me, any recording (whether movie or music or anything else) is essentially a black box of which we can know nothing with regard to the loudness, tonal balance, spatial chracteristics etc. of the recording situation. Likewise, it's utterly pointless to try and second guess the 'intent' of the artist/producer. All we have is the recording as it stands and the reality of our listening environment which we can then tweak so the subjective experience is as pleasing as possible for the widest variety of material. By all means use automated loudness correction if you feel it adds value to your experience, but don't imagine that it's in any way more accurate or 'correct' than manually adjusting tone controls to taste ...