Yeah, 15kph seems unreasonably slow, and I think my kids ride about that fast. Maybe 20kph is better? I usually slow to 15-20kph anyway when there isn’t enough room to give others more than a meter of space when I pass.

So yeah, in kph, I think the regular stretches should be around 30kph, and maybe 20kph around parks and parking areas since there are likely unattended young children and pets around. I can stop very quickly at 20kph.