If you were to break out the concrete at the tub, you would find a p-trap below the 1.5" stub.
Most tubs come with drains centered 14.5" from the back wall. With the overflow drain, you will want it coming up very close to the valve wall.
I would just knock out some concrete and adjust the trap as needed.

: The tub drain is 1.5" PVC stubbed up through the concrete floor almost right up against the wall in the middle of the drain end of the tub and there's no well around it to drop the drain below the floor level.