In the January 2011 data dump, a VoteTypeId value of 15 started showing up in votes.xml, but the readme.txt file only documents VoteTypeId values up to 13. What kind of vote has VoteTypeId="15"?
These are flags that record when a moderator reviews a post or comment. Essentially a "response" to VoteTypeId = 13 (InformModerator), which is not included in the data dump.
I assume they are part of the new system that tracks how frequently flags for mod attention are acted upon, which is why the data only goes back 4 weeks or so (as opposed to only keeping a 4 week history). As it sits, that data doesn't really say much, and may be stripped from subsequent dumps.