Hi Urmas,
Not sure how useful this will be, but when I created the Differences course for 15.4 (available imminently) I used the attached CSV file to bring in 21 roadmap items. I had to first create a 5yr Roadmap, starting in 2018, and then use the Import CSV function (which contains a link to download the CSV template). If you update the attached CSV file before importing it, you can add your own items that will be created when you import the file.
The Roadmapping feature uses your default entity settings for the planning periods.
Best regards,
Sue