For what it's worth, I ran calculations with some new assumptions:

$185,000 loan, 30 years, 4.25%, $383.33 escrow (taxes, insurance, PMI)

$1293.42 payment

At $155,000 left in the loan, probably about $550 - 600 in interest each month currently. Maybe $335 of your payment goes to principal.

$155,000 loan, 15 years, 3%, $383.33 escrow (not sure if PMI would change with a smaller loan but also lower home appraisal)

$1453.73 payment

About $375-400 in interest each month. About $695 of your payment goes to principal.

So refinancing would save you $200 / month in interest. Depending on closing costs, you'd save that back pretty quickly. Not sure why your bank would show $1550 in payments. Personally I'd consider it, because now your rental will be $150 less "cash flow" positive, but you'd be putting a lot more into principal (after escrow and interest) than before.