15lbs bone in rib roast

It probably won't take that long.  Once they are longer than they are thick, it is the thickness that will limit the time and that doesn't really change much no matter how long it is.  At that temp, I would guess 2.5 to 3.5 hours, but you should always leave a little extra time.  I usually cook them a little hotter (275-300) and they take about 1.5 to 2.5 hours. 

When you do the sear, have the appropriate utensils, gloves, and flat surface for when the whole thing catches fire as it often will.  It's no big deal if you are prepared.  Can be disaster if you aren't. 

My first reverse sear made me make a choice. Sear all sides or keep my eyebrows. I choose to backdown the Egg.

Those are all such great comments on being prepared..Utensils, gloves, landing areas etc..I have also learnt the hard way esp as there is almost always adult beverages in the mix.. Good luck and a Happy Christmas to you and your family..

I did a 5-1/3-lb bone-in rib roast yesterday. It was awesome. I just did mustard/spice rub around 6 hours before it went on. Reverse seared, and it turned out great. The crust was tremendous.

At 225f I would expect a much longer cook - yesterday my 5lb rib roast took 4 hours to get to 120f in the middle, 130f at the end ribs, dome temp 230f.

I pulled it, rested it, and then seared the ends at 500f.

The whole cook took about 5 hours, not including the second rest, then I sliced off the ends and re-seared the rare side of those ends for my medium eating wife.

Finished Brian?

Indirect sear:  It is easier and less risky on the roast falling apart, no flames, but you can not see the meat, so it is hard to tell when the sear  is "done" and you have the crust you want.. But you can get heavy smoke if your drip pan is dry with all that fat dripping onto it.

Searing direct you can see exactly what is going on, but there is the chance of inferno and if tied, falling apart.

If you can do the direct, at the right temp and the least amount of lump possible to prevent the inferno, that is the best way in my opinion.

I choose which way to go when I see how much lump is left as well as fat is still on the meat.

Just sear indirect by bumping temp up to 5 or 600. Way easier and safer than direct sear that big piece of flameball.

1:30PM Mountain Time Bump. :-??