From rsync manpage
SORTED TRANSFER ORDER
Rsync always sorts the specified filenames into its internal transfer list. This handles the merging together of the contents of identically named directories, makes it easy to remove duplicate filenames, and may confuse someone when the files are transferred in a different order than what was given on the command-line.
If you need a particular file to be transferred prior to another, either separate the files into different rsync calls, or consider using --delay-updates (which doesn't affect the sorted transfer order, but does make the final file-updating phase happen much more rapidly).
Since --delay-updates doesn't affect the sorted transfer order, how can it help if we "need a particular file to be transferred prior to another"?