Who is running 15 inch slots on the front of their 73 and up a body?

What kind of slots?
Aluminum period wheels with the the kidney-bean slots? or
Chrome-reverse steel slots
And over what brakes?
The reason I ask is cuz;
The flat-spider chrome slots will not fit over disc brakes.
Other than that, everything with the same bolt-circle should bolt on, even Ford wheels.
As to width;
Once you get close to 8" wide, turning can become an issue depending on your ride height, so you gotta tuck it in with a larger backspace.
However, like @SpikeWills69 found out, while backing up turning and riding the brake on factory suspension bushings, the wheel can move towards the front bumper, and rub on the front of the wheelhouse.
But if too much backspace, the sidewall will rub on either the frame or the strutrod. I think on mine, the max backspace was around 4.25inches. For a Zero-offset wheel (to satisfy the SAI,) that makes a wheel width of 8.5 between the outer edges which is normally called a 7.5" wheel.. But I think that you cannot buy a 7.5; your choices are 7 or 8. and both of those will likely come with a bs of 3.75, so then for an off-the-shelf wheel, you are sorta committed to a 7" wheel.
A 7" wheel wants a 7" tread and you might get that on a section width of 8.25. Now in metric, 8.25 is 203mm, so that would be a 203, rounds to 205. So then, the 205 is the right width to run on a 7" wheel.
But, the taller the sidewall, the more wiggle room you have. A 225/75-15 will have a good service life on a 7incher. However, this size tire is about 28.5 tall, which is too tall for the front of your Duster (it looks odd).
A better choice would be a 215/70-15 at ~26.85 tall

If you get an 8 wheel on the front, with a proper backspace, that will want a section of about 235, and to keep the height down it would need to be a 60 series so then, a 235/60-15 is about 26.1 tall.
All numbers above, are my best guess.

You can install wider than these recommended sizes but your tread life at proper inflation pressure, will suffer. To get best treadlife, you the driver, have to experiment with tire pressures. I find the lower limit for me on the front, is about 28 psi. Below 28psi, when cornering aggressively, the tire is already rolling onto the sidewall pretty hard, which is gonna take a good-sized sway bar to minimize, (NOT eliminate). I highly recommend to run the pressures higher, for performance driving, which of course will make the contact patch smaller, making the likelyhood of plowing, all the greater. So the lesson I learned was, for a 50 to 60 series tire, I should run a wheel of not less than 85% of the section width,
thus the numbers are;
195= 7.68, and times .85=6.5" wheel
205= 8.07, and times .85=6.9" wheel, rounds to 7"
215= 8.46, and times .85=7.2" wheel, still a 7"
225= 8.86, and times .85=7.5" wheel, now a 7.5 if available
235= 9.25, and times .85=7.9" wheel, now an 8
245= 9.64, and times .85=8.2" wheel, still an 8

On the back, I run my 295s on 10s at 24psi for long tread life, but because of the rear-steer, it took some getting used. Not recommended for everyone, but that's what it takes for long tread life.