In COMMAND mode, the "one event per second" limitation imposed by Lightstreamer Moderato only affects single keys, hence the snapshot, which is made up of different keys, should flow fast.
However, your snapshot seems to be very large, so the <max_buffer_size> limitation applies in this case.
This setting avoids that the event queue for a single subscription grows beyond any limit.

If you know that snapshots of many thousand events can be expected, then you should increase <max_buffer_size> accordingly.
Note that this may affect all event queues, related to items in RAW mode or with the "unfiltered" flag, for which the Data Adapter event rate fairly exceeds the "one event per second" outbound limitation.
In the forthcoming 3.6 release of the Server, things are going to change and <max_buffer_size> will no longer limit event queues when they are related with COMMAND mode snapshot.