So here, by the way Detective Conan used this way too, is 'my' way to find north easily without waiting 15 minutes. In fact you have to have at least a watch to find north THIS way. In the case it is an analogue watch - you are lucky time-saver. But though you know how to read an analogue watch, it will also work with a digital watch because you can somewhat imagine the needles of the analogue one.
Step 1: Supplies
Here is what you need:
1. a watch (like written in the intro)
2. the sun (you don't have to have a good sight, you just have to barely know the position of the sun)
Step 2: Point
Now look onto the angle between the little needle and the 12 o'clock mark.
Take the middle of the angle and imagine a drawn line from the middle of the watch along the middle of the angle. The imagined line will show you South. In the opposite is North.
Before 6 AM and after 6 PM always take the middle of the smaller angle.
Step 3: Final comments.
The angle must be halved because the earth turns around the sun once while the needle of the watch turns twice (AM and PM).
The method is quite capable, though it works only in the northern hemisphere, but the closer you come to equator the more inexact it will be.