The error 15 when restoring a file is usually a result of the user failing to specify the file to restore properly. If the file is being extracted from a Master Backup, one should be aware as to how the files are written on the tape.
Each file on the tape is written in relative format.
For example a directory is /u/data/payables, it is stored on the tape as ./u/data/payables. Note the leading dot, that is included as part of the path. So remember to include the dot in the path.