At the beginning I thought that this is something common when you use NHibernate with rich applications, so I didn’t pay much attention, but then it became a real headache.

One of the best colleagues notified me about an important note, which is that I was loading other domain objects from a shared  module (which I didn’t really need).
I checked the NHibernate config file, and removed the mapping line that includes those shared domain objects, and the time shrank to 15 seconds!

The moral of the story is that it’s ok to suspect code we inherit from others, other modules or projects, we might not gain anything by doing that, but I am almost sure that we won’t lose!