I am asking for mustachian input - given that every dollar of income from my second job is thrown at my debt car, what is the best way to prioritize these payments so I can get out of debt ASAP and start saving more?
FTFY.
First, I am a huge fan of the basic approach laid out here: tackle your debts in order of interest rates. You just cannot get ahead if you're paying 15% interest on anything.
Your situation is complicated by the car, however. Because your second job requires lots and lots of driving, and nets you only about $150/mo. I am assuming that $150/mo. is after gas, right? But are you considering depreciation? The reality is that the more expensive the vehicle, the more money you lose with every mile you drive. It's basic math: if you have a $40K car that depreciates 15% over the course of a year, it loses $6K in value. OTOH, if you have a $4K car that depreciates that same 15%, it loses only $600. So the problem here is that your fancy car means that every mile you drive is costing you way more than you think.
If you want to get a better estimate of the real cost of driving, use the IRS mileage reimbursement figure (which is usually something like $0.50-0.55/mile). I wouldn't be surprised if the math said that you're actually losing money on your side hustle, because getting to the job costs more than you earn doing it. The only way a side hustle with lots of driving makes sense is if you do it in the cheapest, most fuel-efficient vehicle you can get.
Of course, the problem is that you don't have the cash for a different car right now, and you really don't need more debt. So I am going to modify my standard advice somewhat and agree with Lady SA: cut expenses to the bone, and then split the extra between that 15% loan and the car loan. And that includes the Roth contributions -- a Roth does not get you either a match or an immediate tax deduction, and over the long haul, it is very unlikely that the market will return more than that 15% you are currently paying on that first loan, so until the first two loans and the car are gone, it makes more sense to devote your excess cash to the loans than to the Roth.
In addition, look for a different side hustle that can net you more cash. And if that isn't realistic, then do as much extra work as you can, as efficiently as you can, to maximize the amount you have available to dig yourself out of this hole (e.g., if the problem is a long commute, can you work one 10-hr weekend day instead of two 5-hr ones?).
Finally, congrats on digging out of CC debt on a relatively low salary. I know the hill looks big now, but if you just continue to tackle the remaining loans with the same attitude you used to tackle the CCs, you really can do this.