OTA speeds are sometimes throttled in order to manage traffic and avoid saturating the network - thereby increasing the reliability of the upgrade process. However, if you wish to modify the throttling settings, you can issue an Image Block Response command (Command ID: 0x05) from the OTA Server cluster (ClusterID: 0x0019) with Success Status set to 'WAIT_FOR_DATA', to set a new download rate by specifying the delay between update frames being sent to clients.

For example, to send the Image Block Response command from RapidConnect Desktop, go to the ZCL Message tab, specify the Destination Node, use Cluster 0x0019, Command ID 0x05, with Payload: 97 00 00 00 00 00 00 00 00 01 00

97 = WAIT_FOR_DATA (1 byte)

00 00 00 00 =  Current Time 0 (4 bytes)

00 00 00 00 = Request Time 0 (4 bytes)

01 00 = Minimum Block Period in milliseconds (2 bytes)

See screenshot below: