so sorry, i meant would leaving law school be worth it if it were a T14 school? UW-Madison is not a T14. Transferring up, however, is common in law school. I was just curious if anyone would think it crazy to leave a prestigious law school for med school. Personally, I don't think it is, but med students may have better insight into this.
I left an entire 20-year on Wall Street, where I had attained a high position and made a salary that I will NEVER match in all my years as a doctor (should I be lucky enough to make it into med school). It would have been much more rational to stay where I was, but people's dreams and interests are not always totally rational. I am doing this because I can't get medicine out of my mind, despite having tried to talk myself out of it repeatedly for years.
However, even though I may be following my heart in trying to change careers, that doesn't mean I get to ignore the realities of getting into med school. (I wish I could, because I think the whole system is pretty screwed up, but I'm in no position to change it.) What everyone else has told you is true: med schools are pretty robotic about grades, and a 4.0 from Podunk U will trump a 3.5 from Harvard pretty much every time.
Think about the statistics for a second: most med schools accept less than 10% of their applicants, and some accept less than 5%. Most of the 90-95% who get rejected are eliminated very early on by GPA/MCAT screens: if you don't make the cutoff, they don't read your application, no matter how interesting you are or what school you went to. These screens are pretty much universal at state schools, and nearly so at private schools, except for the very elite institutions like Yale and Mayo. (At those places, they read every application, but the applicant pool is dominated by students with very high GPAs and MCAT scores. So the extra attention given your app isn't going to help very much if you don't stack up well against the competition.) If you DO make it past the screen, you may get a little intangible credit for having gone to a rigorous school, but it won't be enough to seal the deal if your GPA is far below average for that institution. Unfortunately, 3.15 is far below average for pretty much every med school in the US.
I know how you must feel, because I'm going through something similar myself. I got terrible grades at college (an Ivy) because of serious personal problems, but didn't do any of my med school prereqs then. I ended up working on Wall Street, got an MBA at a top school with a 3.8 average, and did well in a 2-year postbacc program. But my uGPA is still low, because it includes bad grades that are 25 YEARS OLD (and don't even include any science courses). Med schools don't care if this makes sense or not--that's how the rules work, and they follow them to the letter. So now that I'm applying, I'm going to be compared to 22-year-olds based on grades that say nothing about how I'm likely to perform in med school--and the likelihood is that I'll be rejected at the vast majority of my schools, based on those grades. I just have to accept that, and do the best I can with what I have to work with.
In your case, I think it would be very unwise to try to apply to med school without going back to postbacc and putting in a solid couple of years taking courses and building up your volunteer experience. As others have said, you need that experience both for your app and for your own personal thought process--this is a such a harsh and grueling system that there's no point putting yourself through it unless you really, really want to be a doctor. And if you rack up a bunch of A's in postbacc, that will raise your GPA and make you much more competitive.
Don't believe those who insist it's impossible to get into med school without a picture-perfect record, because there are many stories of people who have gotten in despite some sizable blemish (low grades OR low MCAT score OR weird past--but not all of the above). But you have to make the rest of your application as strong as possible, you need to articulate a bulletproof rationale for why you want to be a doctor, and you must prepare yourself for an uphill battle. Most of us nontrads here are fighting those battles, and we'll welcome you into our ranks if you decide this is really right for you.