In my experience, if $12k is of significant use to you now, then sell. If the amount does not really matter (because it is so small in comparison to your total assets), then taking the financial risk for more reward can work.
I have been issued stock options at two employers, my DH has had them at three employers. My employers were very large, close to Fortune 50 companies, and DH's were smaller start up types in tech. We have only made money on them once, for a smallish amount similar to the $12k you indicate. It really sucks as the options were worth a lot more money for a while before vesting, for a couple of them, and one we actually bought and held, and it spiked up, but we did not sell in time and they dropped on a single news announcement (the CFO arrested in Germay for stock pumping a different company). Which was a surprise to us, and impacted the share price, of course, depsite DH knowing that the sales funnel for his company was packed.
Anyway.. Stock options are not a guarantee. Many companies issued them to more people thinking they were a great benefit after the first wave of people did very well with them, but the second round (you, maybe) will likely not have the same gains because past results do not indicate future performance, etc.