It's basically because of a memory issue. I just downgraded to 2GB ram on this openvz vps. And the swap can't be changed from 512mb.
Another database at 350MB has no issue finishing. But the 1.5GB db crashes everything.
Because it's MyISAM I apparently can't use --quick / single-transaction.
Any ideas on what can be done? Nightly backups ran fine at 4GB ram.