Connection Latency may be contributing to slower than expected move speeds. Upgrading to 2013 Sp1 for your MRS server and ...

Connection Latency may be contributing to slower than expected move speeds. Upgrading to 2013 Sp1 for your MRS server and setting ExportBufferSizeOverrideKB = '7500' in MSExchangeMailboxReplication.exe.config on the On Premises Exchange server may improve migration speed. The setting is discussed in the get help link