Yes. For example 15.1 is the first level when you go through the door at level 15.
Tha whole thing becomes a bit complicated when you search for Hell levels... 54.12.1.9G.12 is more complex

But it is the same system - door at level 54, vortex at level 54.12, then the vortex at level 54.12.1 (which is the second level, not the first... It is not everything logical^^), levf vortex at level 54.12.1.9 (G=gauche=french for left; right would be D, but is not used...), and then the 12th level - there you can find the Pyramid Pass

By the way: Level 54.12.1.9G.12.1 is level 55^^