the page related to
15.4[2] says
Also, if you are upgrading from a version earlier than 15.1, see
Section E.7.
Is that correct?
Yes, the wording and links are correct.
If you are upgrading from 15.2 or 15.3 to 15.4 there is no “see also” to worry about.
The point of that sentence is not to provide a simple always-present link to the prior release notes. It is to warn about special update concerns if the update is not trivial.
David J.
