Yes, 1.5.x still uses the config options internally. From the docs:
This feature is deprecated in cpg1.5.x or better and can no longer be configured, since it only lead to end user confusion. If you performed a fresh install or if you have never changed this prefix, the option won't show through. Only for those who have actually changed this option and have a config setting that differs from the default prefix, the text field will show at all. If this is the case for you: you're strongly encouraged to change this back to the default value to avoid possible issues in future versions.
It's a one-way option. If you upgrade and you have a non-default value, you'll see the config options on the admin page. If you set them to default, the options disappear. But the config options are used internally, so you could modify the database to change to non-default values and everything will use whatever you set in the config options.
The warning about future versions applies, but I don't think anyone has any plans yet to make this option non-operational in future versions.