Time Machine - Preparing takes forever... (> 6hours) My time machine backup always takes a really long time. I actually don't know what caused the problem... but it's happening since a long time.

It takes about 6hours or longer, it doesn't matter if there are just small changes on the files or bigger ones. It always takes that long. But the backup finishes after that time.

It would be great if you could help me.
Thanks

... ~ %  tmutil status    
Backup session status:
{
    BackupPhase = Starting;
    ClientID = "com.apple.backupd";
    DateOfStateChange = "2020-05-23 17:06:00 +0000";
    DestinationID = "013AD7A7-C1AE-4E9B-A28B-2F8539045349";
    Percent = "-1";
    Running = 1;
    Stopping = 0;
}
How long since the previous backup?

There is a correlation between how much time/how many changes/the size of the changed files and how long it takes to prepare and how long it takes to complete.