Thanks for keeping me updated about this, @Michael Hunter.
I'm with you in ensuring that you'll be able to convert your QuickBooks Desktop to QuickBooks Online successfully.
When downloading a free trial version of QuickBooks Desktop, you have the option to delete or keep your old data. In situations like this, to retrieve your QuickBooks 2015 files, you'll need to restore the backup copy of your company file, you have created any.
Once done, you can now proceed with converting your data by following the instructions found in this link: Move your QuickBooks Desktop file to QuickBooks Online.
You may also see this conversion guide for your visual preference: File Conversion.
If you need further assistance with performing this process, feel free to reach out to our Customer Care Team. They have can run a remote-viewing session and guide you with the steps.
This should get you on track, Michael.
Please let me know how that works for you. I'm here provide you additional assistance if you need anything else. Take care!