Regardless of outcome the habit of investing is better than spending on liabilities.
But 15% is too much for now, more impossible in coming years; let alone 15yrs.
even real estate is saturated now & struggling to give 6%-10% & that too before taxes & expenses.
As economy becomes behemoth, people need to come to senses & realise that double digit rate of return will be mythology.
So instead of fixed 15% u should have a realistic low to high range
Remember that after 15 years, 1 Cr will be equal to 10 lacs only.