you have four options to solve this ORA-19815 case,just work as follow
You have the following choices to free up space from flash recovery area:
1. Consider changing your RMAN retention policy.
If you are using dataguard, then consider changing your
RMAN archivelog deletion policy.
2. Backup files to tertiary device such as tape using the
RMAN command BACKUP RECOVERY AREA.
3. Add disk space and increase the db_recovery_file_dest_size
parameter to reflect the new space.
4. Delete unncessary files using the RMAN DELETE command.
If an OS command was used to delete files, then use
RMAN CROSSCHECK and DELETE EXPIRED commands.