For some time there has been a limitation: A fresh install with Oracle 12c wasn't supported; workaround was an install with Oracle 11g, followed by an upgrade.
A direct install should be possible now (SAP note 2133079) from May 18th, 2015, but it seems your SAP installer isn't aware of that.
So I can think of two possible solutions:
1) Get a newer installer, if available.
2) Go the old way, Oracle 11g and upgrade afterwards.
regards