For us metric-impaired, 30 km/h ~ 19 mph.
In the United States, school zones with children present are generally 15-25mph. fit adult humans run at 8-9 mph.
If it works for Finns and they like it, great. Americans would not accept speed limits so low.
European cities are way denser though. So you have less view of the area because of smaller streets and very densely parked cars. I found the limits in the US comparable to what I'd drive in Germany in cities. Maybe Sedona is a one off, but it felt very familiar. For me, wider roads and better view means I can drive 50-55kmh and that's what the limits were. Smaller and denser street means 25-30kmh which is around 15-20mph? We even have the "you can make a right turn at red after coming to a full stop" with a special sign (a green arrow). So I think the speed limits are ok and it doesn't feel too different for me. What is not ok is the rampant ignorance towards laws. Red light and stop runners in bigger cities and such. Lots of bad drivers out there.