The info files are not distributed with automake15. They are in RawHide 1.6, so this is just in the unlikely case you'd ever want to make an errata release.
I am aware of the issue, however at the time I decided that it was too much trouble to patch the texinfo to generate automake-1.5 info files to not conflict with automake-1.4. (For autoconf253 there is only one info file, so it is just a matter of renaming the info file.) Perhaps if there is an errata for automake15, the info files can be put into the doc dir.