SCSI drives can write data from 60 to 160 Mb/s. Of course there is some OS kernel overhead. Divide your 15 Gb of data to the write speed of your drives and backup time will be estimated.
For the restore, again drives speed first + ORACLE DBA speed to resolve db crash scenarious :-)) . Even the most seasoned DBA's panic when production db goes down, so get your best estimated time, multiply it by 2, and scale up once. So if you usually restore for 1 hour - that might take up to 2 days (according to Murphy :-)) )
Hope that helps,
clio_usa - OCP - DBA