CoIoT update_period can be set to 15 - but still operates at 30sec

I can set the update period to 15 sec at reding it in status also show afterwards the 15, but the real intervall stays at 30s.
I'm using the Home Assistant Integration (via CoIoT). I set the value with http://<IP>/settings?coiot_update_period=15 and it is accepted by listing it afterwards.'
But looking at the intervall it still is 30 sec, also setting e.b. 60 sec does not have any impact. I want to avoid migration to pure MQTT, loosing the cloud functionality.