Add v3.15.0 to CHANGELOG [ci skip]
Add v3.15.0 to CHANGELOG
[ci skip]

(cherry picked from commit e3bd1e55a899997d1707efaeb162f1ec061e5f91)

givanse/ember.js,knownasilya/ember.js,mfeckie/ember.js,tildeio/ember.js,elwayman02/ember.js,GavinJoyce/ember.js,elwayman02/ember.js,asakusuma/ember.js,elwayman02/ember.js,GavinJoyce/ember.js,mfeckie/ember.js,sly7-7/ember.js,asakusuma/ember.js,elwayman02/ember.js,mixonic/ember.js,miguelcobain/ember.js,stefanpenner/ember.js,fpauser/ember.js,givanse/ember.js,sandstrom/ember.js,tildeio/ember.js,sly7-7/ember.js,sly7-7/ember.js,sandstrom/ember.js,stefanpenner/ember.js,sandstrom/ember.js,knownasilya/ember.js,fpauser/ember.js,mfeckie/ember.js,fpauser/ember.js,GavinJoyce/ember.js,miguelcobain/ember.js,asakusuma/ember.js,emberjs/ember.js,stefanpenner/ember.js,mixonic/ember.js,miguelcobain/ember.js,miguelcobain/ember.js,givanse/ember.js,tildeio/ember.js,GavinJoyce/ember.js,knownasilya/ember.js,givanse/ember.js,fpauser/ember.js,mfeckie/ember.js,emberjs/ember.js,asakusuma/ember.js,emberjs/ember.js,mixonic/ember.js