I use WP8548 with FW 07.04.06.00 and Legato 15.10.
At the moment it looks like it is not possible to push data immediately to the server with LWM2M. The data is not sent to the server until the server request the data.
Is this a limitation in the protocol or will it be enhanced in future releases?
An option is of course to use MQTT for the application data and only use LWM2M for device management.