It's nice to have you as part of the conversation, @mommie-salami,

I can share some insights about installing the software on different computers.

If you're using a single user license and is not using the file simultaneously, you're able to install QuickBooks on different PC. However, doing this does not automatically sync the data on both locations. You can, however, create a backup of your company file and restore it to the other PC using your USB. Let me guide you through the steps:

Step 1: Create a backup copy.

1. Launch QuickBooks for Mac 2015 (if you haven’t already).
2. Go to QuickBooks.
3. Choose Preferences.
4. Select Backup.

Step 2: Restore the file.

1. Locate the backup copy and double click the .dmg file.
2. Drag the company file (with .qbXXXX extension) to the folder where you want to save the file.
3. Drag the Attached Documents Library folder (if applicable) to the same folder as the QuickBooks company file.
4. Click the copy of the company file saved on the desired location or go to File > Open Company.

However, if you are using both PC's at the same time, and would want to sync your transactions automatically, it is best to purchase a secondary license to enable Multi-user mode. This feature ensures all users can access the file at the same instance. To know more about this, please checkout Step 5 of this article: Install and set up QuickBooks Mac Desktop

Please feel free to post an update below if you have additional questions. I'll be more than happy to help you at any time. All the best!