When I originally wired my house in Ca. I ran separate circuits to each room. Each room has at the most 5 or 6 outlets. The kitchen and bathroom are not at issue here. I've added two extra rooms but have run out of breaker space in the main pannel. I want to combine circuits by adding an electrical box near the main box and running the 12-2 wires from two old rooms into the new box, joining them, and runing one wire out to 1, 20 amp breaker; thus freeing up 1 breaker. I would switch out all the 15 amp breakers and outlets for 20 amp b & os. We use mostly led lights so the combined amps should be low enough not to over load. Anything wrong with this plan; would there be problem with codes?