WebStack 1.5 does not have so far any uninstaller.
Testing it regularly, I needed to be able to quickly delete my current version and install the new one, so I kept the command that does that:
rpm -e sun-rrdtool sun-php52-pgsql sun-wsbase sun-php52-suhosin sun-apache22-sed sun-apache22-jk sun-wsadmin-base sun-apache22 sun-mysql51 sun-php52-mysql sun-jcollectd sun-collectd sun-php52-idn sun-php52-xdebug sun-apache22-perl sun-memcached sun-mysql51lib sun-php52 sun-python26 sun-apache22-security2 sun-apache22-fcgid sun-php52-memcache sun-php52-tcpwrap sun-wsadmin sun-php52-apc sun-squid sun-lighttpd14
Just wanted to share it in case some of you need it as well :)