It's better if you get the main campus of CUSAT. Apart from that indeed there is much competition in International School of Photonics but for special courses like what you want is 5-year Integrated M Sc. You may get the seat and it entirely depends on the counselling day. Suppose some students are not getting the main campus they will opt for good colleges with good courses.  

Chances are high. Keep hope that you will get. Also, you prepare yourself like choices courses in your mind what you will opt for if you're not getting that.