Is there a test environment where I can test SDAC 15-minute MTU?

Yes. The Auction Member Test environment is available every day for multi-resolution MTU testing.  Members can test both the Trading UI and the Auction API.  For more information on how to access the Member Test environment please visit: About SDAC 15-minute Member Test 

For the Market Data API there is no test environment, but comprehensive documentation is available here: https://data-api.nordpoolgroup.com/index.html. For support, please send your questions to: [email protected]