Can a person with high blood pressure 315/100 without medicine for 2 1/2 years have mind strokes and or demetia?

Yes: Hopefully that is not your true blood pressure, I have never seen a BP that high in 15 years' worth of medical practice; the answer to your question is that if you haven't had a stroke, mini or otherwise, so far, you are lucky. You need to get that BP under control and asap.

Yes: ...And BP that high would tend to lead not only to "mini-strokes" but also to stokes that end your life quickly. If you were lucky enough to only have mini-stokes then multi-infarct dementia would soon follow.

High bo: Elevated blood pressure can predispose to stroke and possible dimentia . Readings of 315 systolic ate somewhat unlikely.

Yes: Yes, both strokes and dementia are likely. However, a consistent elevation in blood pressure to that level is unlikely and somewhat incompatible with life in my opinion!