First, I apologize for jumping in without having read your post carefully enough to realize you're a pro, and what that implied about your situation. Instead, I read deltadoc's post and oldpappy's and sort of reacted to what they were saying rather than thinking your problem out. I would have talked some options -- including hot oven start to finish.
The hot oven I get -- you're going to have to watch the roasts carefully and use a thermometer. As you know a hot oven is unforgiving and those tenderloins will be moving faster than an 12 year old Chinese gymnast, > 3deg/min once thery're over 120F. I'd consider investing in a few digital probe on a leash types for this.
The other downside of a high heat roast is the outside cooks so much faster than the inside. However a tenderloin is thin enough that a rest will resolve most of the unevenness, besides some gradient is attractive. If you're cooking a minute don't forget to include at least 7 minutes resting time in your estimate. Are you roasting off whole tenderloins to order?
Your time estimate seems very optimistic to me, but you know how big your tenderloins are, I don't. I think of a whole, trimmed tenderloin as going at more than 4 pounds. If yours are much smaller as implied by a 15 minute roast estimate, you may be cooking doc's chateaubriand. Send him a comp card.
Your proposed sequence of first, sear; second, slather and rub; third, roast is new to me. Off the top of my head, I hate it. You're either plowing the same furrow twice, and trying to build a bark (slathered rub in a hot oven) on top of a crust; or going in two different directions at the same time. Not to mention wasting the one benefit which comes from a pre-sear.
You don't need a sear if you're cooking at 450. You won't save time. 450 is its own sear. How brown and tough do you want the outside, anyway? If you want to pan roast the darn thing like a big steak -- which is fine, leave the mustard off the outside of the meat. Then use the fond in the pan along with some mustard to make a pan reduction. Otherwise, there's no $%&!ing point to the sear.
Worse, if your slather and rub don't crust, you'll have sort of deviled goo on top of crust. Sounds like rack of lamb I had at a bad chain restaurant. It was one of those miracles of bad cooking you wish were restricted to your relatives. I wondered at the time how they did it. Did I mention I just hate the idea?
The normal sequence as these things go is: first, season; second, sear; third, roast. Note, not only is the sequence changed, the slather is gone. If you want some sort of slather try a few tbs of red wine and worcestershire sauce, 50/50, on the roast while it tempers. It takes about 5 minutes, before it starts to combine with the meat juices and form a syrup. Before seasoning (salt and pepper is not a rub), turn the roast to make sure it's evenly coated. Don't forget to use kosher salt. It will make for a much better textured crust, because it clings to the meat and does a much better job of drawing juices to the surface where they can crystalize. Yet another set of benefits to this sequence is the seasoning will mark the fond with its particular characteristics, and will begin the flavor-layering process in the pan sauce.
Going back to your sequence, my native pessimism aside, there's nothing quite like actually trying it. Rules are made to be broken, right? If you've done it before or you're about to do it for the first time, let me know how it works. I'm a pessimist, but a hopeful, interested pessimist.
Beaucoup Important: The one thing no one's mentioned, is: truss the roast. You'll get better shape, more even cooking, and (oddly, and don't ask me to explain) faster cooking. Besides, "Eat ees zee FRAHNSCH way! Eat most be RAIT!" That's how it was explained to me in a kitchen that turned 100 chateaubriand a week -- every one of of which I tied.