Hey,
When the result will be declared they will give all the required notification regarding admission process. The process for ALL INDIA 15% is carried out at http://www.mcc.in you can register here and fill up the choices you want!
Regarding the cutoff it depends on state if you go through 85% state quota which varies greatly from being 490 in west bengal to 570+ in rajashthan. All india 15% has cutoff of around 575+ for General cateogory.
I hope you got your answer
Thanks