I've never actually mixed anything for either theater or DVD, but I do descriptive video (mixing narration into completed sound tracks for the sake of the visually impaired). Basically, my job is to match levels with whatever programme I happen to be working on. This means that I sit all day and watch the Master to make sure I don't blow anything out.
Sadly the average mix level tends to run the gamut. It really depends on the kind of show/movie and the era in which it was made. Recent reality shows are L1-Ed bricks with a constant level of -10. The movie Black Hawk Down was similar, with sustained peaks as high as -3, but an average non-action dialogue level of about -20, action dialogue was give or take -10. A River Runs Through It sat at somewhere around -25 to -28, the very occasional peak at -6, and even rarer sustained peak at about -10. The reason for the difference is the date that the L1/L2 were invented, and simply that DAWs can deliver a much greater dynamic range than tape.
As a general rule though, it looks as if most films end up at -20 to -22. Most TV sits around -12 to -16.
The station I work for likes the final product to come out with a dialogue level of -20-ish, and a sustained peak of -10, one shots to -5 or so are OK, but only on the odd occasion. This means that i often have to alter the dynamics of the original. Personally, this breaks my heart. I hate mussing up other people's hard work. But it's what THEY want, so that's what I do.
If I understand you correctly you're printing to DVD but it's going to be played in a theatre, yes? If so, your dynamic range can be much greater because the system and the room (for the most part) has been designed to accommodate it. I may be completely wrong in this, but as long as you're not in the red or reaching for the volume knob in the quiet bits, you should be fine.
So unless you are being asked to mix something that is network television produced to go to their DVD distributor (in which case I would ask for their technical spec sheet), I have to go with Andres' level recommendations here. At the very least, I wouldn't worry about peaks at -15 or -12db. You have a lot more headroom than that.
– Karol Urban Nov 19 '10 at 21:03