I think you are confusing DD-WRT, which is a Linux-based third-party-developed firmware with no connection to the D-Link company, with the official factory firmware provided by D-Link.
But to answer your question, no, such minor DD-WRT build changes like from r15704 to r15747 don't have change logs. They are usually small bug fixes ported by BrainSlayer from the main branch. No new features or anything like that.
You can, however, see all revisions in the DD-WRT repository here: http://svn.dd-wrt.com:8000/dd-wrt/timeline
Note that sometime the descriptions don't say very much.