Do Muslim brothers in Bangalore need to pray qasr salah if they stay less than 15 days?

I am a native of Hyderabad but for the last 9 years I am living in Bangalore due to my Govt. Job. I am working here in Bangalore on a Regular (Permanent) post but the position can be transferred to other places in India any time by the higher authorities. As part of my job work, I have to travel frequently outside Bangalore to different places across India. I also go in Jamat every month. My question is: Do I need to pray qasr salah in Bangalore, if in between my two travels I will be staying here for less than 15 days or I have to pray full salah? I am asking this because I am confused as few Muftis have told me that I am muqim of Bangalore as I hold a permanent job, other Muftis told that unless I declare Bangalore my permanent place of residence, I will be considered as Musafir if I travel frequently with less than 15 days stay in Bangalore and if during two travels, I stay for more than 15 days then only I will be Muqim. Please give a detailed reply in the light of Quran and Hadith and Fiqh. The question is very important as there are at least one lakh Muslim brothers who are from different parts of India but doing jobs here in Bangalore and travel frequently outside.