Well- here is my advice, rest your legs before you go (don't quit running altogether, just run in a way that won't hurt your legs), and then when you get to OCS, do your best to not think about the pain. In my platoon, all the candidates with stress fractures were sent home. However, those candidates developed stress fractures suspiciously early, and seemed like they were just looking for a way to get out of OCS.
Basically, no candidate in my platoon seemed to get stress fractures past week 1, (one kid was even sent home because he "was in high possibility of developing shin splints", aka, he just really wanted to go home and cried to the doc to send him home). We also had one candidate- an enlisted corporal no less, fake multiple heat casualties to get sent home.
On the other end of the spectrum, my final rackmate (and Farkle's cousin) had one of the worst cases of shin splints I had ever seen, and put up with them all throughout SULE II. While he wasn't all that slow of a runner, he finished dead last in the platoon for the final PFT because the pain, but he still completed the run. He also never reported to sick call for them. It's just one of the many gut checks you will have at OCS. You want to stay as healthy as possible before you go to OCS- but when you do go to OCS, it's game time. You should keep running until your leg literally cracks in half.
If the pain is too much to bear, you can always go to the corpsman, and say that you are hurting (but don't say you think you have a broken bone), and he will give you motrin for the pain.