DIAGNOSIS No, that's excessively slow. A healthy K-Mini should heat and give a steady blue light in roughly 90 seconds. The prolonged heating indicates either severe limescale insulating the thermostat or a failing heating element.
FIX Address scale first—it's the most probable cause.
1. Run a full descaling procedure (see first answer). Heavy scale acts as an insulator, forcing the heater to work longer to reach temperature.
2. After descaling, time the heat-up cycle from a cold start. It should be noticeably faster.
IF THAT DIDN'T WORK If descaling doesn't improve the time, the heating element is likely degrading. There's no repair for this. The machine will still work but will get progressively slower and may eventually fail.
HEADS UP Using distilled or softened water can prevent scale, but Keurig recommends against pure distilled water as it can affect taste. Using filtered water is the best compromise for longevity and performance.