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Without knowing his mileage or what oil he's using, I'd still suggest he
should check / replace his PCV. If it's stuck open the oil vapor will
'disapear' all by itself.

'Curly'

If it is not the PCV, then it is something worn in the engine.  The
consumption rate (~1 qt/1500 miles) isn't terrible awful but it should
be better with only 155,000 km (100,000 mi) on the car.  Has the car
been well maintained?

Probably not worth spending money on it now (except for PCV valve).
Just watch it carefully and add oil as needed.  It could go a long
time without getting much worse.

Your oil consumption as stated is only 1,500 miles per quart, which
isn't too bad except for the fact you've got less than 100,000 miles on
the engine. I've got the same consumption level, but then I've got
283,000 miles (456,000km).

However, if I were you, I would get an accurate reading on your oil
consumption before panicking. Most people have no idea how to properly
check their oil consumption.

The distance between marks on the dipstick is one liter, or 5% more than
a US quart. Make certain you're pushing the dipstick in all the way, and
check more than once.

Do this:

1) Drive car for at least a half-hour.
2) Park car and leave overnight.
3) In morning, BEFORE starting car, check oil level on stick and note
it. DO NOT ADD MORE OIL. If level is not close to top, discontinue test.
Top up as necessary, then resume from Step 1.
4) Drive car 1,000 miles (1,600km)
5) Immediately before parking the car for the last time, drive it
EXACTLY as you did in Step 1.
6) Leave car overnight in precisely the location it was in Step 2.
7) Check oil as you did in Step 3, and make note of the level. How far
did it drop on the stick after 1,000 miles?

This level of precision is necessary to ensure proper readings. Ideally
you're starting with fresh oil, so any water in the old oil will be
gone.

Variables can greatly affect the reading on the stick, so it's important
to eliminate them as far as possible.

Variables to eliminate:
1) Old oil, which may have water in it. A long drive can burn up the
water, causing the apparent level to drop.
2) Different driving conditions prior to shutdown. Cool oil has a
tendency to not quickly run down into the pan, causing a lower level.
Hot oil will run down more completely, causing a higher level.
3) Different parking spot angles, whcih can tilt the level towards or
away from the stick.

Coolant temperature gauge readings are NOT an indicator of oil
temperature.

Do NOT check your oil at the gas station when filling up. That's the
worst place to do it.

None of the above means anything if your consumption is normal; it only
becomes important once your consumption becomes a problem.