This is a perfect place for a facepalm emoji.
I mean, I get it. When everyone else around you is doing it (and frankly, they probably can't afford it any more than he can), it's a legitimately hard thing to not buckle to the pressure. Especially since it's a huge indicator of your "value" these days.
But for a $1500+ monthly payment... Yeesh.
But the OP's brother is not alone, the problem is there are lots of 35, 45, 55 and 65 year olds making similar decisions.
Not the worst? Perhaps technically. That loan payment is going to be an absurd burden on that young adult for a period of time they can barely relate to. Especially if they lose their job for any appreciable amount of time, or encounter other sudden costs (such as rent being jacked up).
Remaining employed full time for 7 years at the age of 19 with a wage good enough to make $1500 vehicle payments is... well, I would have failed that test.
I had a 300 hp turbo'ed Miata while still a college student at 21 years old and a few years later a 380 hp Dinan M3, all while living with roommates or cheap apartments. Once I got a bit older and lost interest in cars like that my vehicles were mostly econoboxes on leases or lightly used entry level luxury cars.
It's a very different thing than someone who is established in life with real responsibilities spending an outsized portion on vehicle expenses.
Perhaps you're right though. I went to uni etc so didn't have that kind of cash until much later but might be different for those who leave school earlier.
Children in the US can begin work at 14, and assuming he either bought or was gifted a low value project car that he began putting money into from the age of 15 when he would have been eligible for his learner's permit, he could have been earning for up to 5 years before his latest job.
It's also not unheard of for children to own vehicles before they're old enough to legally drive them. There are no license or minimum age requirements for ATVs in some states, and in rural areas, some children begin using them to commute (off-road) as soon as they're large enough to operate them. One of our local schools had stables for horses, and another had chargers for golf carts. While helmets weren't legally required, the schools encouraged them.
In 2020, McDonald's paid cashiers just over $11/hr, so if he worked there just 500 hours each year from the ages of 15 to 18 (10 hours a week), he would have been able to earn over $20K before he was 19 without much effort - or earned all of that in a single year after graduating high school and working full time.
If he was a car enthusiast who wanted to work at an auto shop, like NAPA Auto Parts ($15/hr base), he'd have been able to earn $15K in two years working the same part time schedule. He also would have received full state and federal taxes back each year, so it would have been near to gross earnings.
This isn't really uncommon here. Everything costs something, so most people have to work starting from their teens. Insurance, for instance, is expensive for young men, so if he hadn't been paying on his car's current cash value (or at all) to control costs, he may have received nothing on the vehicle after it was totaled, but he wouldn't have owed anything. By 19, he'd already be used to living paycheck to paycheck.
And while there's no limit to what someone can spend on their car, I'm also taking $15K as an embellishment. $8-10K is more normal for moderate aftermarket work, including labor, and some people buy, sell, and trade up often. I'd believe a teenager spending $3-8K on used aftermarket and then telling people it was "worth $15K", estimating it would have cost around that if they'd bought new and had the work done professionally.
On the other hand, you're not wrong about its capabilities. And honestly, if it's just groceries, one could easily go for a used car or hatchback.
If anyone knows of a left hand drive, all wheel drive diesel hatchback, let me know. That's my unicorn car. I'm not even sure something like that exists.
"Ah no but the used truck doesn't have a touchscreen or a radio with bluetooth or builtin GPS" /s