My point is if booked into AMS or CDG on DL metal, those awards would qualify for 15%. Yes, the last segment from AMS/CDG to/from OSL would have to booked separately on another award which would not qualify for 15% discount or simply booked as a revenue fare (SAS will be in Skyteam by then so AF/KL/SK would be potential Skyteam carriers).
Getting a Skymiles award into AMS/CDG should also be easier to find than all the way to OSL. But as with revenue fares, they will not be particularly cheap for summer travel and look to be in 170K range for a roundtrip in Economy from AUS. Awards out of competitive gateways like BOS and JFK are cheaper (due to cheaper revenue fares) with Skymiles awards in the summer to AMS/CDG in the 100K range for Economy. With DL Amex, you would get 15% off those mileage amounts when flown on DL metal.