Inside of each campaign report, you can generate a deeper report to get a good understanding of which ones of the interests you've chosen to build your audience is performing the best.
If you want to see them, here's what you need to do:
Select an ad set in your campaign report, and look in the action bar's drop down list:
Once you click on the Interests Stats, the following window will open:
In there, you can see all of the Interests from your audience(s) - and you can verify that going in the Audience tab of the report:
These stats should help you explain which interests helped you build the most relevant audience, leading to ads that work well!
Keep in mind that the data available will only go back 7 days.