15,000 online? Yes - that is a great start, but represents (by my count) about only 20% of the published newspaper pages (at least in America). I don't know how many Trove covers in Australia (it's a lot), or even if you add up all the pay sites such as Newspapers.com or Genealogy Bank (as two examples) - what that does to the percentages.
What about the other 80%? They are either still only in newsprint, or have at least been microfilmed, or are lost forever.
But my historical newspaper researching colleagues almost always forget to check which newspapers are available in libraries, either in newsprint, or microfilm, as previously mentioned.
But - and this a big but - there are subscription databases that libraries subscribe to that libraries provide FREE to their patrons.
I have written some recent articles about these databases and the list is below.
The moral of the story (at least for this article) is that you must look into what your local (or nearby) library offers in terms of these databases for you to search.
You just might be amazed. And furthermore, depending on the library, you just might be able to search these library-only subscription databases from the comfort of you home in your PJ's!
Try these on for size (and ask that library what they offer for you)