Lightroom 6 upgrade

So, all that being said.

Are you trying to upgrade perpetual to v6.14?

or

Are you trying to go subscription?

Lightroom CC (20150 was an early subscription version, not the perpetual. At the time Lightroom 6 was offered as either perpetual or subscription, with subscription having more capability. Lightroom perpetual eventually ended life at version 6.14 ( that is six point fourteen, not sis point one four)

https://laurashoe.com/2017/10/26/whats-in-a-name-clearing-up-the-confusion-over-lightroom-application-names/

The subscription Lightroom is now called Lightroom Classic and is currently v10.4. Do not confuse current Lightroom Classic with a separate product called Lightroom ( aka Lightroom Desktop, Lightroom Ecosystem, Lightroom Cloudy, and by us old farts as Lightroom POS), Lightroom Classic is what v6 became, current Lightroom is a lesser product that stores albums on the cloud and photos on the cloud instead of catalogs on the computer, photos on the computer (normally)

The subscription programs are installed using a seperate application called Adobe Creative Cloud Desktop App.

Agreeing with @AxelMatt , and adding that the only way to have Lightroom CC 2015 is via a subscription, which because it is so old, Adobe no longer offers a subscription to it (they do offer subscriptions to their current software).

Lightroom 6 is the latest perpetual version. There are no further upgrades available.

You can buy a subscription (for example the Photographer Plan). Then you have to install the Creative Cloud desktop client first.

https://www.adobe.com/creativecloud/desktop-app.html

From this you can install Lightroom Classic (actually version 10.4). When you try to open your old catalog it will be upgraded to the new version.