The DHCP Database Files section in the DHCP online Help states that the default DHCP BackupInterval is 15 minutes.

The correct default is 60 minutes:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DhcpServer\Parameters

BackupInterval is a REG_DWORD value with a range from 1 to 71582 minutes.

A related entry is BackupDatabasePath, a REG_EXPAND_SZ value, that specifies the folder where the backup copy of the DHCP client database resides.

NOTE: The backup can be on a different local drive, to facilitate recovery.