By how much can I trim back the connectors of 1.5" PVC fittings?
I see that the tee in your drain pipe is already cemented in place, but if you can redo it, you can do what they did in my house (not home right now, so I'll have to remember to get a picture later).

What you can do is turn the tee and drain fitting to the sides and use two elbows and three short pipes to connect them.

The only tool I have to illustrate this right now is MS Paint, but it should be better than nothing. This is the view looking down from the top (or up from the bottom):