How can an extra $900/month for 15.5 months save $190K? Remember, the interest savings is really only 60%-70% of the annual interest expense (assuming you fall under SALT). You get to write off at your effective tax rates.
I'm assuming your loan is a jumbo based on the projected $190K savings. My position on paying additional principal depends purely on your job and economic security. There is the present value of the $900/month surplus and the interest savings isn't noticeable until later in the loan; a lot can change in the 5 - 8 years before meaningful reductions appear. Additionally, your monthly payment doesn't go down (unless you refi again) so if any catastrophic events occur, you have less cash.
If you compare the present value of money and are good investor, it may make sense to invest and pay principal as you see fit. Not hugely adverse if you drop an extra $5,400 principal payment 6 month later vs spacing out $900 each of the first 6 months.
Also, I would consider the market and historical appreciation in the area. While many would say paying off a loan as fast as possible is wisest, having liquidity outside your home and working for you could be a better path.
