Is a 15% Turnitin similarity acceptable in APA 7?

Yes, a fifteen percent similarity score is generally considered very low and acceptable in APA 7, but since your professor set a strict ten percent limit in the rubric, we need to get that number down for you. It is completely understandable to feel stressed when you have done everything right, like paraphrasing and citing correctly, but a technicality with a massive author list is holding you back. Think of Turnitin like a hyper-sensitive metal detector at the airport; sometimes it beeps at a harmless belt buckle, which in your case is just a perfectly legal APA 7 reference list entry. Since your deadline is next Monday, you have plenty of time to fix this. First, check if your Turnitin submission settings allow you to filter the results. There is usually a small funnel icon on your feedback studio page where you can check boxes to exclude the bibliography and quotes from the match overview. If you check those and your score drops below ten percent, you are golden. If you cannot change those settings yourself, just take a screenshot of the report showing that the match is purely from the twenty-author citation in your reference list. Send a quick, polite email to your professor explaining that your actual writing is original, but the long APA reference is inflating the score. Professors are human and they understand how these tools work, so they will likely appreciate your honesty and proactive attitude. You've got this, so take a deep breath and keep up the great work.