It really depends how fast you expect them to fly. But let's look at how your changed world will affect them.
The equation you're looking for is:
Area = (lift force)/(half velocity * velocity * air density * lift coefficient)
Or mathematically:
$$ A = \frac{L}{0.5 v^2 \rho C_L} $$
$A$ (area) is the number we're looking for.
$L$ (lift force) must be equal to the mass of the person, in order to support their weight. People on earth average 62kg. With all the exercise from flying, they might average a little lower in that world.
$v$ (velocity) is the take-off speed: the speed at which the forward movement through the air makes the lift cancel out the person's mass.
$\rho$ (air density) is specified as 1.5 times Earth's.
$C_L$ (lift coefficient) is approximately 1, and depends on the angle of attack and wing shape. You can assume their wings are decently well shaped, so can ignore this term. Changing this to make thrust is, basically, what flapping does.
Wing loading on an Earth hang glider is as high as 6.3 kg per square meter, and the takeoff speed is about 15 mph.
From the equation above, we can see that the wing area is proportional to mass ($L$), and inversely proportional to air density ($\rho$). In other words, wings need to be larger when there is more mass; and don't need to be as large when the air is denser.
So we can multiply the needed area by $\frac{0.6}{1.5} = 0.4$. So 6.3 kg per 0.4 m2, or 15.75 kg per square metre.
That's roughly a quarter of human bodyweight, so you'd need four square metres for an average person. Two square metres per wing. Assuming folded wings like birds have, that's certainly achievable.
Now, let's push the limits. Adults with anorexia have a BMI below 17.5. So let's aim for that, as the acceptable limit of thinness. When $M$ is mass, and $h$ is height, $ M = h^2 \times 17.5 $.
This scales with the square of height, so height is definitely not a good thing. So assume 1.5 m (approximately 4'11").
$$ 1.5^2 \times 17.5 = 39 \space\text{kg} $$
That needs only 1.25 m2 per wing!
Something else to note, though, is that lift improves with the square of the velocity, but linearly with area. So if you double the speed to 30 mph, you can quarter the area: in a 30 mph wind, you could hover in a trenchcoat.
If you halve the speed, you only need to multiply the area by $\sqrt{2}$: so for a normal weight person, you can have gliding at 7.5 mph with 2.8 m2 each side, which is still in the range of achievable, and means they could take off in a breeze or at a run, without needing to jump off a hill. For our petite skinny person, that's only 1.8 m2 per side.
Acrobatics would require higher velocities, but that's what a dive is for! :D