Server migration

I've asked this before, but now it's time to move one server to another, I can't delay the operation anymore (the older server is failing)

Both server are pretty old: 1.2.15

Probably, faster way would be to rsync all mailboxes from the older server to the newer one. I can start migrating everything while running then, stop the older server and sync only what is changed, keeping downtime at minimum.

Any better solution ?

No, server upgrade is not possible. Not at this time. It's too time consuming and I have to move asap.