Hello there, @AZEmbroiderer,

Good to see you here in the Community.

Yes, you can uninstall QuickBooks versions 2015-2018. Please take note you have to create a back up of your company file then restore all company files to 2019 to ensure you can open the files to the newest version. Also, you have to verify and rebuild the company files before converting them to 2019.

Top of that, if restore back up company file to 2019 is successful then that's the time you will uninstall them. Let me help you how you will restore your company file.

Here's how:

1. From the File menu, select Open or Restore Company.
2. Select Restore a backup copy and select Next.
3. Choose Local Backup and then select Next.
4. From the Look In drop-down, choose the location of the backup file.
5. Select the backup file from the folder. The file name should appear as [Company Name].qbb.
6. Select Open andthen select Next.
7. From the Save in drop-down, choose the location where you want to save the restored file.
8. In the File name field, type a new file name. (Note: The Save as type field will automatically populate QuickBooks Files (*.QBW).
9. Select Save.

Once done, please read carefully and respond to any messages that appear before restoration begins.

Please refer to this article for more information and detailed steps on how to back up your company file: Restore a Back up of your Company File.

Let me know if there's anything else I can do for you, I always have your back. Thanks for reaching out, wishing you and your business continued to succeed.