A prompt will state that the key is already in use. Click .

Searching for a "Parallels Desktop 15 activation key" is understandable, especially if you have an older Mac or need compatibility with a specific legacy system. However, the reality is clear: this software version is obsolete and unsupported.

Even if you find a working activation key, you face a harsh reality:

: For new users who have never owned Parallels. This is a standalone license that doesn't require prior versions.