Drain line sizing for laundry and sink- code confusion

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I would like to add a utility sink next to my washer. Right now, I have a 2 inch laundry standpipe going into a p trap, a cleanout, and then into the slab a 2 inches. It is vented by a 1.5 inch vent through the roof.

My city uses IPC code, and from my limited understanding IPC 406.2 says that once I add another fixture to the washer line (like a sink), I'll need a 3 inch drain. I'm I interpreting that correctly?

Secondly, International Plumbing Code 802.4.3.1 allows for adding a sink to the standpipe of the washer. If I do this, will I still need a 3 inch drain or could my 2 inch drain be sufficient?? Right now, the sink is more that 30 inches from the standpipe, but I think moving the standpipe would be easier that tearing into my foundation to increase the drain line to 3 inches. It's not clear to me what the drain size requirements are for a 802.4.3.1.

Any other ideas or suggestions are appreciated.
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