My understanding of this is entirely academic. I buy my first pure rental property here in a few months.
Your specific situation is going to be something you have to figure out for yourself, but here's how you go about it.
Right now, you have a certain amount of rental income. You are able to offset that rental income by deducting your rental expenses. That's everything except for the principal part of the mortgage payment. So...
Property taxes, insurance, gas, sewer, water, property mgmt, yard, any maintenance, phone, business related expenses, and depreciation on the house.
You add all those up (can use numbers from last year).
Then figure out what tax bracket you are in (and are going to be in).
The only change to you is going to be reducing that deductible amount by that mortgage interest.
Let us just assume you are in the 25% tax bracket.
You used to have (x+$15k) roughly in deductions. Now you only have x deductions.
So you will pay 15*.25 or $3,750 more in taxes, but you'll have 15k in income not going towards the taxes. So you end up positive $11.25k in terms of cashflow. And also, you know, in terms of net worth (it is a real gain).
But wait!
It takes additional capital investment to eliminate those mortgages, so we need to look at the opportunity cost. I'm going to ballpark your outstanding mortgage balance at [a lot].
But I'm also going to note that you have "cash laying around" that can pay off five thousandish in interests worth of principal at maybe 4.12 (which is what 130k or so? That's nuts!), and say that you just keep tons of cash laying around.
So your opportunity cost is relatively low, and so likely you'll be better off.
There's also a risk reduction factor to be considered by eliminating debt, such that it is usually worth considering if there are only marginal opp cost considerations. As in, vacancy still impacts your total returns, but it is a lower risk to your month-to-month solvency.
But yea, this can get very complicated, and you're going to want to look at what your return on capital is before and after. In some cases it is going to be much improved, and in some it would actually be worse.
The advantage a FIRE minded person might think about in paying off, is that if you were barreling towards FIRE and getting close, once you no longer have a regular gig income, and you get down to the 10% or 15% bracket, the deduction is worth less. Particularly if you were to pick up a RE license and got to treat the rentals as cap gains income instead of earned (which may be something I just made up and not a real thing).