According to the documentation, I have created a fresh install
That's not what the documentation is suggesting. In fact it says quite the opposite.
I can't imagine when nor why the documentation (that I have read many times) became more important than a living breathing person like myself.
We're human beings as well, and we give support freely without getting paid or getting any other way of compensation. We can expect that you do read the documentation instead of anticipating that we're going to explain the same issue over and over again to each lazy person like you.
Does anyone have helpful suggestions on how to upgrade my MySQL database tables correctly from 1.4x_ to 1.5x_ so I can use my current data?
Yes, I have a suggestion: you re-read the upgrading section and do exactly as suggested there: replacing the existing cpg1.4.x-files with fresh cpg1.5.x files and then running the update script will perform the needed database changes easily. Stop dragging your feet and whining about your missing skill level: it's not hard to read that little upgrading section and respect the simple description there what you need to do instead of coming up with wrong assumptions.
I discovered that changing the table prefix in the include/config.inc.php is not a solution.
Nobody said that you should do that.
I discovered that exporting the old database and importing that data into the new database doesn't fix the problem either...
Of course not. Nobody said so neither.
even if the new data is contained in correctly named tables with the prefix cpg15x_. In short, I am personally not capable of correcting this issue with the documentation available.
Instead of blaming the documentation you should learn to read it properly. Don't blame others for your inability to read the docs properly. A very big effort has been put into the documentation, and you're welcome to help us improve it even more by posting your additional information. However, just saying that the documentation is bad is not helpfull. You can hardly expect help with an attitude as confrontational as yours.
Additionally, you have failed to do as suggested per
board rules, so what do you expect? If you came here just to troll, then you succeeded. But I won't tolerate this any more.