The rules for CSS 2015 say :

"The Question Papers in Urdu or other Pakistani regional languages (Punjabi, Sindhi, Pushto and Balochi), Persian and Arabic should be answered in the respective languages unless otherwise directed in the question paper."

Whereas the 2014 Rules said :
"The Question Papers in Urdu or other Pakistani regional languages (Punjabi,Sindhi,Pushto,and Balochi) Persian and Arabic should be answered in the respective languages OR IN URDU/ENGLISH unless otherwise directed in the question paper."

So it appears to be confirmed that for Persian and Arabic , the whole paper will have to be attempted in Persian and Arabic respectively in CSS 2015, as the CSS 2015 Rules have done away with the option to attempt them in English or Urdu.