I've looked at the circuit and I have a couple of comments:
You need a higher voltage transformer than 14VAC or a much larger filter capacitor, to get 15V out at higher currents. To regulate proberly at 1.5A the LM317 needs the input voltage to be at least 2.25V about the output voltage at the absolute minimum, for optimum performance it needs to be at least 3V.
Note that the other characteristics on the datasheet are specified with the output at 3V lower than the input voltage.
Attached, is a simulation of a 14VAC transformer, with a bridge rectifier with a 2200:mu:F capcitor and a 1.5A constant current load connected. The output voltage dips below 14.4V which will produce a huge ripple voltage on the output of the regulator. Increasing the capacitor value to 22000:mu: increases the minimum ripple to 17.6V which is fine even though you won't get the best from the regulator. This assumes that you haven't got anything connected to the LM7805, if you're going to connect a 1A load to that as well, you need a huge 33000:mu:F capacitor.
Another thing is how reliable do you expect the voltage drop of those diodes to be? They won't be exactly the same as the reference voltage of the regulator and will drift a bit as the temperature changes. You can get round this by using another op-amp configured as a difference amplifier that looks at the voltage between the output and common pin on the LM317 and inverts it to the negitive value.