Building a battery powered +-15V DC Power supply PSU
If you set your boost converter to produce precisely 30 volts (not 33 volts) then you have achieved the outer rails but not the mid rail. The mid-rail can be made with a single 15 volt regulator. I would choose a buck regulator for doing this because it will generate very little heat.

So, your isolated 30 volt output becomes +15 volts. Your isolated 0 volts becomes -15 volts and the buck regulator would produce a mid-rail of 0 volts.

It makes no difference if you regard these three voltage as 0, +15 and +30 OR -15, 0 and +15 - your circuit will not perform any differently.

Buck regulator idea. This one shows a 12 volt output but can be adjusted to provide 15 volts by altering R1 or R2: -



There are plenty to choose from.