That depends upon whether you are running classful or
classless routing. If running classless, it also depends upon whether
or not you have the 'ip subnet-zero' option enabled. If running
Also, with that subnet mask, .15 would be a broadcast address
and cannot be used for a host address.
Steve, great question. If you are studying for the Cisco CCNA exam,
then yes, they are now valid. Pre- 2005 exams would have considered
those invalid. As the other posts mention, this is the ip subnet-zero
command, which is on by default starting in IOS version 12.1.