This is a great question. The answer, by the way, is "no, TL15 ships are not TL15 from bow to stern".
As I said in another post, I do think game rules should be interpreted as simplifications of "reality". But that doesn't mean said interpretation should gratuiously ignore everything the rule implies.
There's a game rule that says "The TL of a ship is the TL of all its components, from the hull to the computer software" (I'm paraphrasing here). Common sense says that it is possible to mix components of different tech levels. But unless there's a compelling reason to think otherwise, the game rule is presumably a simplification of reality, not a total transmogrification of it. If the rule says that all ships have uniform tech levels, it's a little much to claim that few or no ships have uniform tech levels. Surely the existence of the rule implies that most of the time tech levels are uniform, and only in special cases are they not.
The next logical question is "what defines a ship as TL <whatever>?", to which I am forced to reply, "the hull".
Or perhaps the tech level of the shipyard that builds it?
From a design point of view, there's little about a hull to indicate a tech level, except perhaps integral armor; however, that's the most likely answer.
Well, the material that the hull is composed of might provide a slight hint of its tech level.
This is probably a rules-specific answer, by the way.
I don't see how it can be. If an answer adheres to the rules, it may be rules-specific. But if it's based on ignoring some of the rules on a "common sense" basis, you can't very well clain that it's rules-specific.
You figure that its size forces some rethinking of purpose, and I'd say you're right.
My suggestion is that it was sector-level project, not an Imperium-level project. As such, the ships may have been partly funded by several duchy navies. (That would explain why the marines on the
Luuru don't all have BD training; they're Duchy of Regina marines, not Imperial marines
).
What about the Black Globes? Well, the
Kinunirs were also secretly meant to be test beds for these new Black Globes. It was a "hide in plain sight" scheme where the Black Globe mountings were "sold" as mountings some other kind of experimental device (a much more mundane and boring device). Only a few of the
Kinunirs were ever fitted with a Black Globe.
You also imply another question: why weren't they all produced at one shipyard? I don't know, but I'm sure we could come up with any convenient reason. (For example, this was an initial trial batch which was squeezed into the cracks of production schedules).
Oh, I'm sure some explanation can be found. My point was, however, that whatever story is selected, it will affect the background history, and that the
existing background story almost certainly won't work.
Now we've firmly crossed into rules-specifics. With the rules I use, most small starships are built in this manner. The oddity would be an all-TL15 ship, or all-TL9 ship.
You'll have to explain that a bit more. These rules you speak of, are they your personal house rules or do they have anything to do with canon?
And why in the universe would most ships be built with a melange of components running the gamut of tech levels?
So the conclusion is that, indeed, shipyards have little desire to build stuff below their TL without good reason...
That's not a conclusion, it's a thesis.
...and can't make stuff above their TL as well as higher-TL worlds...
And that's a truism.
...What they can't produce locally, they can import.
They can indeed. However, that adds transportation costs to the cost of the components, and since higher-tech shipyards are able to build lower-tech hulls cheaper (there's a motive for building lower-tech hulls (and components too, for that matter)), such ships would be at a competitive disadvantage.
And finally, shipyards, due to their nature of being shipyards, build hulls locally, at their TL;
Or lower.
...when a ship is built at a shipyard, the keel is laid down locally at the mainworld's TL. (That has interesting results with, for example, TL 8 class A starports).
When a ship is built at a shipyard, it is built with components manufactured locally unless special circumstances makes it reasonable to do otherwise. That's MY supposition.
Thus the Imperial Navy would prefer to build its best ships at its best shipyards. But smaller support ships not intended for the front lines perhaps have more leeway.
The Imperial Navy will want to buy its ships from wherever they get the most clang for their cred (that's futurespeak for 'bang for their buck'
). What that would be depends on a lot of factors.
Hans
And it still makes little sense as a "Battle Cruiser" (except in name) in the HG universe 
