I have never seen 504.00 oil with sulfated ash at 1.5.It's 1.5. This is one instance where reading a PDS is helpful, if you're substituting something for 508 00 you should be aware of the SA for the oil - such as for Mobil 1 ESP.
There is no way oil would be DPF compatible. Regardless what VW put as limit, purpose of 504/507 oil is to be compatible with DPF. So, by that VW limits sulfated ash level.