If you haven't had a problem, and have no intention of getting into steeper terrain, or carrying more of a load, you're probably OK. Given that it is used and about 10 years old, it may or may not have the stock shoes on the brakes. Especially at your weight, but also due to the potential age of the brakes it is likely worth at least investing in a good set of shoes. There are several opinions on what constitutes good shoes, but I think I can safely narrow your choices to shoes SwissStop Green or CoolStop Salmon. And you should inspect and probably clean your rims from time to time, depending on how clean and dry the roads are when you go riding.

The two risks inherent in rim brakes are that
1) if you do overheat them sufficiently you can cause the front tire to blow off the rim [possibly mitigated by using an aramid (Kevlar (TM) )-bead tire].
2) you will have slightly poorer braking when wet [quality pads (see above)] will make wet braking close enough to the same as dry that the risk at the tire-road interface is greater than that at the brake-rim interface.

It is because of 1) above that most folks planning to do loaded touring - which for us would mean roughly 360-375 pounds for riders plus gear (not including bike) - use a drum brake when riding in steep terrain. You don't need to - but it is easier (descending - harder by a couple of pounds climbing). If you don't have a drum brake and you go down a sufficiently steep hill that presents the need to slow down or stop - either a stop sign at the bottom, or a sufficiently tight curve, or even surface conditions that don't warrant the speed you might otherwise go - you may need to come to a full stop from time to time in order to let the rim and brakes cool off. As Sheldon Brown says, "For pure stopping power, good rim brakes, properly adjusted, can stop a tandem as well as they can stop a solo." It's repeated slowing that's the issue, especially just leaving the brake on.

On our tour last summer I would have used the drum once had I had it installed. But we managed. The rim was hot enough to be quite uncomfortable to touch, but nothing failed. This was a case of a (very) steep hill with a stop sign at the bottom and a 30 (20?) MPH speed limit (park road). I wasn't sure how much in excess of 20 MPH above the limit I should let it go, so I slowed way down two or three times on the way down, and then just let it go in between.

Bottom line: at your weight, if you're going to be in seriously steep terrain - other than straight and smooth - I would recommend adding the dreaded drum. Overheating your rims can cause catastrophic failure in the form of the front tire blowing off. Overheating a disk brake can reduce its effectiveness, just when you need it most (which is true of rim brakes if the tire stays on). But if you're willing to slow down to a stop and let your brakes cool when you get to a point of risking overheating, your current system or disks will do the job.