I also like to select 15 dB for some extra bass but without twhomping the whole house.
The value chosen here mostly represents what level whoever mixed the original content was listening at. For movies, often 0 is the best choice (although as I understand, nowadays it's not so much a given fact). For much else, 10 is usually a good value. But there aren't any rules (except for movies, and even then it seems like the rules are sometimes broken). Of course, if you don't use DEQ and rely on your house curve, you might have even more trouble adjusting it on the go for different content. Eventually, as far as I understand, the loudness correction depends on the difference between the mastering level and the actual level, so as long as that difference is constant you could keep the same curve. But of course, there is no way to guarantee this difference is actually constant even if you always listen at the same level.
Seems like the only way to never need loudness compensation (or be able to keep a constant one integrated in the target curve) is if you always (or at least when caring about the quality) adjust the volume level until everything sounds balanced. Although for for different content that level could end up being a different one.
The only way I understand of to find the dynamic EQ offset needed, is to find the level at which everything is balanced, set the offset to that value (hopefully it's close to either 0, 5, 10 or 15), and then adjust to the desired listening level. Or just set the desired listening level and try find the offset which makes everything sound the most balanced. Of course, at least for me, it's often difficult to decide what's "balanced", because it's not always obvious how much bass was originally intended, although in some extreme cases it's easy to tell if the bass is overdone.
In the end, I just set it to 0 for movies and 10 for everything else, and forget about it unless something sound really off.