I just printed some 1mm thick test pieces.

I loaded the 15 and 30 tooth gears into cambam and generated a profile with the built in generator and it was exactly the same outer and root diameters (just a bit more lateral clearance in the root) so I suspect you're right about the ring gear - unfortunately cambam doesn't do ring gears (I've bumped a thread asking for them).

Measured OD on the 30t gear is 40.0mm and 21.3mm on the 15t and the tooth tip diameter on the ring gear is 72.7mm and the root diameter is 76.4 (near as I can tell - it's a bit flimsy)