I am afraid a faster solution is not possible. The F!Box needs up to 15min to determine the connection state for a device. Let me quote AVM’s support page:
Smart home devices such as FRITZ!DECT radiator controls, FRITZ!DECT sockets, and FRITZ!DECT Repeaters function according to the standard DECT ULE (Ultra Low Energy). Devices that use this radio standard only communicate with the FRITZ!Box at greater intervals. When the FRITZ!Box is restarted, for example after a FRITZ!OS update, it may take up to 15 minutes for the connection to be automatically reestablished.