In 15k, do the following -
1) Change the head unit to Pioneer - 7k
2) Change front speakers to 2 way components (JBL/Auditor/Kicker) - 4k
3) Buy JBL/Powerbass 4ch amp - 4k
4) Wiring + Fuse + Labour - 1.5k
On second upgrade -
1) Rear co-axials on boot door - 4k
2) Kicker/Ground Zero/JBL sub - 5k
Connect 2 ch of amp for front speakers & bridge 2 ch for sub.
I would advise you to install the speakers on rear door panel instead of boot door. I have done it in my Scorpio & you can see the pics in my thread here
I am also from Mumbai & I have done the install from Ramie.