I don't claim to have read every post on this thread. I just wanted to post a little info.
First, the main reason to do IBR is to get loan forgiveness either through the IBR (or the newer ICR-A version) at 20 years or through PSLF at 10 years, not to pay down the interest. In fact, it's unlikely that most IBR payments actually cover the interest. Since the loan is based on your income, and not the amount of the loan or the interest rate, it has no relationship at all to the interest that is accruing. Some current residents (and even some students) still have some subsidized loans, but there are no new subsidized loans. The government is paying the interest on those while you're making IBR payments. I don't think that's the case with forebearance. So if you have subsidized loans, you absolutely want to be doing IBR instead of forebearance.
Second, you don't pay 10-15% of your income toward the loans. You pay 10% of what the government considers disposable income, which is dramatically less than your gross income. A typical resident is paying $100-500 a month in IBR payments. Do the math and you'll see. This calculator is a great resource:
http://studentaid.ed.gov/repay-loans/understand/plans/income-contingent/calculator
Put in $500K in direct loans at 6.8% (yea, I know you can't get that much at 6.8%, play along please) and an income of $45K. If you're single, your payments are $558.50 a month. If you're married with 2 kids, your payments are $357.50. If you're married and your spouse is also a resident making $45K (without loans), then you'll pay $1241.50 a month if you file jointly and only $558.50 a month if you file separately. (Notice that little strategy).
Third, while you might not be making a huge dent in your loans as a resident/fellow, I don't think ignoring them is a great idea. Student loan interest rates are really high, and at an average rate of 7.5%, you'll owe twice as much money after 10 years of compounding.
Fourth, you won't get to deduct student loan interest as an attending because you make too much. You get this deduction without itemizing, so it's pretty valuable as a resident. So you want to make sure you pay at least a couple hundred bucks in interest a month so you can maximize that deduction. (Plus getting the deduction further lowers your income and your required IBR payments.)