Migrate Teams Chats with "All messages" needs lot of time, preserve of already migrated messages if re-migrate later with (only) "last 15 days " option?

Hello,

we currently perform an Teams Chat pre-migration (appr. 150 Users with the TEAMS CHAT MIGRATION ADDON licenses) to see, if all works and if there are special problems during such a migration.

But, this migration task currently runs more then 11 hours and shows a progress of only 11%.

The migration task has the option to migrate ALL messages - I suppose that is the reason for this long duration?

We try to perform the real migration one week later - could I then use the Chats migration option "Messages within last 15 days" to shorten the Chats migration task, because the older messages are already migrated and preserved?

As the documentation shows "Chats can be migrated multiple times. During remigration, new messages are added to previously migrated chats in the target, and new chats that were not migrated before are migrated.": that means, every new Teams Chats migration task (with changed days option from ALL to only 15 ) will not remove the already migrated messages? Or will the 15 days option remove older messages?

Regards,

Rainer