OK, per Charlotte's catalog, an upright 3" PVC combo (the one piece fitting you used at the closet bend) has a height (from mid-line of the barrel to the base of the hub) of 7-9/16". And a 3x3x1-1/2" reducing street san-tee has a height of the side entry (from the end of the spigot) of 3-1/4". So together the mid-line of the 1-1/2" side entry would be 10-13/16" above the mid-line of the 3" horizontal drain. Which puts the top of a 1-1/2" pipe at about 11-13/16" above the 3" horizontal drain.
In other words it should just fit under your joist, including a little extra for the hub thickness. You'll obviously a few Fernco 3005-33 or the like to make up the new connections once you cut out some of the existing PVC. And if some reason there's a snag with the above geometry, there are other options, such as using an upright 3" wye, then the street 3x3x1-1/2" reducing san-tee (so the barrel is at a 45), and then a street 45.
While you are redoing that, it looks you don't have enough room to make that cleanout useable? Not sure what plumbing code you are under, but the IPC requires 18" of clearance in front of the cleanout plug. So rather than use a combo at the WC for the cleanout, I think you'd be better off with a LT90 for the closet bend and a downstream 3"wye for the cleanout, where it will have 18" clearance in front of the plug. With the wye rolled up maybe 30 degrees from horizontal so that the cleanout is above the center line.
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Cheers, Wayne