SPP plans are great when there's a significant discount. But, with a two year hold period, anything could happen. I would recommend you contribute to this and sell it in month #24, as soon as you're allowed to. Then you can use the money you make to pay down your student loan debt. Figure out how much you need to pay off the CC debt before the interest activates, then contribute the rest to the SPP. In two years, you can have a steady stream of SPP sales to pour into debt payoff.
An 85% buy-in is a great return, as long as the stock is stable or increasing. That's a 17.6% ROI on your money (15/85 = 17.6%). But you do have the added risk of tying up a portion of your income for two years, and you still have to pay taxes on the money you make that goes to an SPP.
It looks like you made a mistake in calculating liabilities, I get a total of ($115,087.90). That's a lot, but you can repay it as your career evolves, so long as you keep your standard of living the same as your income increases. You're saving $1900 a month right now. Pay off the CC's first to eliminate them before the interest rates kick in next year. If you put half of that in SPP, and half to CC repayment, that will take 10 months. Then get to work on your student loans in order of interest rate. Good luck!
