Will there be changes in the System Price methodology and will System Price be published in 60, 30 and 15 min MTUs?

Official prices from Market Data API will be provided in 15-minute. However, additional endpoints will be created to offer new price and system price indices in 60-minute and 30-minute intervals for users who need them. This update will be a non-breaking change for existing customers. 

Similarly, a new indices pages will be created in the public Nord Pool market data page and in Data Portal (under https://data.nordpoolgroup.com/auction/day-ahead/)  where these other granularities will be published.