I see the drains are 2 and 3 inch. I have 1 1/2. is it OK for me to reduce it to that size? Is it against code?

Shower drains should be 2 inches . Do you mean your existing shower drain is 1 1/2 ? If so you can probably reduce and use your existing line but check with building officials in your area to be sure. If it were me and my existing drain was 1 1/2 I would change it over but that's just me . If your installing a totally new shower then the drain should be 2 inch. Post back if I missed anything. GOOD LUCK, AC