Q: HOW DO I PREVENT PHOTOS FROM IMPORTING MY IPHOTO LIBRARY

The library won't be automatically converted, and if a version of it designed for Photos gets created anyway, the modified one will only be visible to Photos.

In any case, you'll be able to go on using iPhoto as you do now.

(125846)

Don't open the Application. When I tried Photos out, I had to do the import manually, there was no automatic import. If you are concerned, make a copy of your iPhoto Library and move it outside the Pictures folder.

If you don't want to import these files then the response will depend on if you have done this already.

Can you confirm this?  I can show you how to remove, and also prevent form doing it again.