I assume that you want to know how much to invest in an SIP over 15 years to arrive at a corpus of Rs 20 lakhs. The answer would be to invest between Rs 3,000 to Rs 4,000 per mont in an SIP for 15 years. This assumes your return will be tween 12% and 15% per year over the long run.
To find out which funds are best for this, check the “Wealth Builder” section in Jama.co.in
Check the goal calculator here: Goal Calculator for Mutual Funds