Your existing FHA loan will drop MIP when you hit 78% of the appraised value at the time of closing. You are forced to pay a minimum of 60months
A Streamline will add slightly to the loan amount. Therefore, will extend the MIP dropoff point slightly. But is still based on the same 78% above calculation.
From the time of purchase, with a minimum required down payment and no extra payments towards principal, it takes about 11yrs on average to drop MIP or hit that 78% Loan-to-Value ratio.
So, if you put down the min. down payment at the last closing, you paid on the loan for 2yrs, I would assume you will have 9yrs to pay MIP. You might add another year to that by increasing your balance through the streamline.
Your Loan Rep should be able to accurately estimate when it will drop off OR some Truth In Lending disclosures will give you the estimated date and it's accurate as long as the original value is entered correctly.