monthly, and a return of 15% you can end up with ₹ 15 lakhs plus.
Make sure you only invest in direct plan mutual funds ,else the return could be ₹ 12 lakhs with the ₹ 3 lakhs going to the distributor.
Consider a good multicap fund for your investment horizon. To exactly know what fund suits you, take this free risk profile here.
Here is a list of multicap mutual funds.