Read for yourself how Cardinal Burke has left no possibility of doubt, none, that disobeying Canon 915 is always a mortal sin. The reason is that disobeying Canon 915 is ALWAYS to commit the sin of sacrilege against the Eucharist, and is ALWAYS to commit the sin of giving grave scandal to the public.
Cardinal Wuerl refuses to obey Canon 915.
So here we have the Pope giving an important role in the selection of bishops to a man who has been living PUBLICLY in the state of mortal sin for many years.
Then why does the Vatican II Church allow individual bishops to decide on whether to follow it?