Is 15/10.5 blood pressure considered dangerous. My uncle has a high blood pressure from 5 days but he don't want to see a dr& he take no medicine.

High. His blood pressure is on the high side, specifically the diastolic or the lower value. I suspect he has also symptoms and that will be grounds to seek medical attention as his symptoms may not be caused by his blood pressure, but rather his blood pressure being reactive to another condition.