Update nightly test-set to use -sv-comp15 configuration and SV-COMP15
categories, this is more relevant now than -sv-comp14.
The file name is kept as it is because the BuildBot requires it.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14621 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c