Hello!
I was over of the 10'th reboot, when I gave up and reinstalled wheezy (I was unable to
modify the starting processes as well. I wanted to do it, because I hate starting into gdm3,
and the system was not able to handle update-rc.d -f gdm3 remove command. I mean gdm3
was disappeared from rc.x directories, but systemd was still boot me into gdm3.)
So, firstly the slowlyness was not because of the first boot (because I tried more than 10times)
Secondly, I can not say how the system would act for commands given by Michael (because
I moved back to wheezy)
The only thing I can add to this topic that the problem came not because of a
bad apt-get dist-upgrade, because boot was slowly even if I installed a
completely new jessie.
Based on your answers, it seems my problem is an exception and not the rule.
But it seems something is not okay with the new jessie, that's sure.