The DL Amex Reserve Club does not provide you with a Sky Club membership, it only provides Sky Club access. It won't get you into international partner lounges. However, you will be able to enter them when flying internationally with your Delta Platinum (Skyteam ElitePlus) status.
Can you elaborate on this...??? I wasn't aware that PL Medallion status has any access to any partner lounges based on that alone; I thought you can only access the lounges overseas if you are travelling in Business Class ON that specific airline.....?