Adaptive Server provides a script for backing up sysmessages before upgrading to 15.5.
Use uninstmsgs.ebf to back up sysmessages before running instmsgs.ebf. Refer to the Post-upgrade tasks, section.
Installing Adaptive Server version 15.5 overwrites the current Adaptive Server software. Before installing, verify that your databases are error free and that your $SYBASE directory is backed up.
To ensure that your database is error free, run dbcc checkdb, dbcc checkcatalog and dbcc checkstorage before loading any new Adaptive Server binaries, including the master database. If the dbcc commands reveal problems, check the Error Messages and Troubleshooting Guide for actions necessary to fix the problem. If the error is not listed in the manual, call Sybase Technical Support.
After you have verified that your database is error free, back up your $SYBASE directory in case you need to roll back to the original version of the software.