So long story short, need to create some space for a new more efficient HVAC duct setup in my crawl space. The new duct run goes under my guest bathroom which includes a sink, toilet and tub all along the same wall. The plumbing runs right through the center of the space and I want to tuck it up between the floor joists for a few feet over before dropping down and tieing into the end of the main line.

Is there a minimum drop for the tub and toilet before you should elbow it over? Toilet is 3" and rest is 2" dropped down to 1.5" right before connecting to the tub/sink vertical run.