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)