Will this make movement smooth?
no, because a completely new level is loaded.
Cause if I got you right, the method you showed me, will just place player at the new level, with distance from door from old level's door. Am I right?
yes
how to make this without loading new level, cause I'll make all levels(rooms) in one big level.
simply set the player's position to the next start position (and add the distance to it). In that case, the transition is smooth.
I need to be able to move smoothly between door, as I said before. I need to be able even to stop right between doorways.
You can always walk everywhere between the triggers. You just have to make sure, that the look of the transition area and the RELATIVE placement of the triggers/start positions are 100% identical. If not, you'll notice the position jump...
