Double fixture fitting question

[Ntcarson]

Hey guys - Just a quick and, hopefully, not too dumb question. I'm putting in a 2" drain -> double fixture -> vent for back to back bathrooms. Off of the double fixture, left and right, I will come over a few inches then 90 out under each vanity for the trap. At what point along the way should I convert from 2" down to 1.5"? I was planning to stub out at 2" then add a trap adapter. Is this the best route, or should I save some space in the wall cavity with 1.5" out of the double fixture?

Thanks,
Neil

 

[Mr tee]

Assuming the vent is only for the lavs, use a 2 x 1 1/2 x 1 1/2 x 1 1/2 double fixture tee and stub out 1 1/2.

 

[Sponsor]

 

[Ntcarson]

It will serve as a vent for a standup bath a couple of feet away, as well, so I'd like to keep the vent 2". I've already got a couple 2x2x2x2 double fixtures, so should I just put a 2x1.5 bushing in each side, then 90 and stub out from there? Thanks!