-- UPDATE FOUR--
today my wires finally arrived but in the meantime I read about the Pi's 3.3V rail and their maximum current draw.
So I came across this problem that the maximum current the Pi can handle on its 3.3V rail is 51mA (correct me if I'm wrong), which is reached after 3 LEDs lighting up. Take e.g. 19:49 and you will have 15 LEDs burning each drawing 15mAs.
Since this is my only Pi and I can't afford another one I will rebuild the circuit a little bit but I am not yet sure whether I want to use transistors or go over the 5V rail which can handle 750mA to my knowledge.
Anyway, Yann Guidon / YGDES who is a follower of this project answered my questions on how to optimize the circuit and we will team up in a second project which will have an optimized version both of the circuit and the code to be more compact.
I will now upload the source code how it came to my mind when I first thought of the project. Be careful not to re-build my circuit yet because it could potentially damage your Pi!
When I was testing if everything works my Pi2B did not have any problems or instability problems but I never had more than 7-9 LEDs glowing at the same time and to be honest I do not want to risk executing the code at 19:49!
I hope you had fun following the project (this is not the end) and I will soon post a link to our (Yann and I) new project. Stay tuned and feel free to follow me for more easy but practical stuff done with the Raspberry Pi.