I just added * fedora-23-i386 * fedora-23-x86_64 * fedora-23-ppc64le chroots target to Copr.
You need to got to "Edit" tab in your project and enable it.
If your project need bootstrapping, then easiest ways is to add: https://copr-be.cloud.fedoraproject.org/result/NAME/PROJECT/fedora-rawhide-$... to "Repos" entry and resubmit your SRPM for F23 target. It will use BR from rawhide, which is now very similar to F23.
copr-devel@lists.fedorahosted.org