Bitcoin Core compiled "bad91-dirty" version
The "51bad91" may be a bit misleading here, it's just coincidence that it says "bad". It's actually just the most recent commit on the 0.15 branch, https://github.com/bitcoin/bitcoin/commit/51bad9195eb435200626beccbaf6b60774a4a894

The -dirty suffix is added during the build here:
https://github.com/bitcoin/bitcoin/blob/master/share/genbuild.sh#L38

I believe that just means that the most recent commit on the 0.15 branch (the 15bad91 commit) was not tagged (i.e. part of the actual 0.15 or 0.15.0.1 release, it is on that branch in preparation for 0.15.0.2).

Thus you should be able to avoid the -dirty suffix by checking out the version tag rather than the branch, i.e. checkout v0.15.0.1