I'm actually not so sure. Even if 100% of the signups to the new version came from users trying for the first time, the previous version being essentially free could have got the app a lot of publicity in tutorials, recommendations or even just showing more highly rated or higher in the download charts.

All of that could increase discoverability of the version with only 15 minutes free trial, so it would be essentially trading sales for advertising.

That said, 2 weeks evaluation on a tool you might use only once effectively means it's just free. Those who might have a need say once a month might just uninstall and reinstall it, and feel completely justified because they didn't get their 15 days, only one day.