There is no guarantee how long it will last. Here in the US, car manufacturers must supply enough new cars every year to replace every car built 15 years ago. I know this because I did a study on battery industry. It happens that car manufacturers are the largest consumer of batteries by a long shot. Compared to the typical life span of the US car, your car is near it's life. That doesn't mean it can't last longer. Good preventative maintenance and care can extend the life of a car. Many times cars get put out of commission simply because it becomes uneconomical to continue repairing.
Your transmission could have an issue that could get worse. It could be a hydraulic pressure problem, accumulator leaks, valve, or clutch problems. I recommend taking the car into a transmission shop. Sometimes it is an easy fix and could save the clutches if fixed early. When the clutches wear out (due to slipping), then the entire transmission will need to be rebuilt. At very least check the trans fluid. You can inspect the color and smell for burnt smell. The trans fluid should be red. If really dark or black it is a sign that the clutches are slipping.