It will all depend on the operators that you are using, the hair amount and the amount of details on the hair. I can´t tell without looking into your scene.
Some advices. Don´t increase the viewport count to 100% if you are ready to render.
You mentioned that you have 3 million polygons, is this for the hair only? If so, this makes me think that you are rendering the hair as polygons, which you should not do unless you are using an unsupported renderer.
Jeordanis Figuereo (Product Designer. EPHERE Inc.)