1 1/2" Copper Shower Drain NG in MA

I demolished my 2nd floor tiled shower. After removing the copper pan, I was left with a 1 1/2 copper drain pipe. I know this is not code in MA. Wanting to do things correctly (not sure if I am going to have it inspected), I opened up the floor to trace the drain pipe to the stack. It is threaded 1 1/2K to the cast iron.
I'll try to post a picture.

What can be done to make it a 2" line?
Thanks,
Michael

To answer a few questions before they may be asked;
The drain line is about 5 1/2' long.
The large pipe to the right of the 1 1/2 copper drain is from the toilet.
The two pipes on top of the copper drain pipe are the hot and cold water supply to the shower,
they make a 90 degree turn in the direction of the shower right (I guess) after the drain for the toilet.
Hope this helps.
Michael

Somehow that toilet pipe looks like it runs up hill into the same pipe that the shower drain is going into. Is that an optical illusion?

Yes Bob it's an illusion,
There has never been a problem with smells or draining (that a quick snaking didn't fix). I've had to snake the shower drain a couple of times in 20 years. The house was buillt in the 60's and we moved in during the 80's.

pipe

The shower drain appears to be connected to a 1 1/2" tapped opening. if so, then the only option is to remove the tee and change it to one with a 2" opening. If what we see is all there is then the shower drain is both undersized and improperly installed.