Egyptian government officials and news are reporting similar numbers:
“Ten people were killed in violence between Christians and Muslims in Cairo on Tuesday night, the state news agency reported on Wednesday.
The agency quoted a senior health ministry official as saying 110 people were wounded in the violence.”
http://voiceofthecopts.org/en/news/ten_killed_110_injured_in_egypt.html
I’m sure those numbers are right. I’m just querying the 15000 number