Upgrade or alternative upgrade?

Hello everyone. I recently started playing Heroes 5 on the anniversary edition and, out of curiosity, I sometimes browse this forum. I have a question about building a Fortress for the Dwarves. Respected Lordesat mentioned above that it's possible to build Dragons by the end of the 2nd week. However, no matter how I try, I never manage to do it; the fastest I can achieve it is on the 1st day of the 3rd week. Let's set aside the issue of resources and money and consider a typical build order. If I understand correctly, to build Dragons, you need a city level of 15, and 2 weeks of 14 days each. If you build something every day, that's 14 levels! How can you possibly fit 15 buildings into 14 days?