Alexander, what you have is called a multiwire circuit and is in fact two separate 15A. circuits. The neutral carries only the difference in loads between the to hot legs (remember that the voltage on these legs is 180 degrees out of phase). There are a couple of possible downsides to his kind of circuit. If for some reason the neutral connection should come loose, things can get very weird. Second, is that there is an increased noise coupling between the two legs since they share the impedance of the common neutral. This might be of concern if, say, you had refridgerator or other compressor on one leg and a computer or other sensitive equipment on the other. The longer the run of common neutral, the more coupling. Most electrical equipment should have no problem.