Wire sizing from breaker box to bedroom
A 15A breaker (AFCI) is not just permissible in this situation, it is required because of the #14 wire in the circuit. You should make a note somewhere near the panel indicating that circuit has #14 wire in it and to not replace the 15A breaker with a 20A. Alternatively - and this is the much preferred way to do things - just use #12 throughout and put a 20A breaker on. 

However, if at all possible, keep your receptacles and lights on different circuits. If you trip a breaker you won't be left in the dark!