The pixel pitch is 0.16mm, which may be rather small. For example a 27" 2560x1440 monitor has 0.23mm, and that is getting towards the small, depending upon your eyesight.
You can scale what Windows displays on each monitor. How well that works is dependent upon the scaling ratio.
You may find that even with 2.5K, the effective pixel pitch may be too small, compounded by less than optimal mapping into the available pixels. Such mapping works best with pixels that are much smaller than the effective pixel size you are trying to achieve, which means much better than ‘retina’ at the distance from which you are viewing.
Unless you have another use for such a small-pixel monitor, you may be better off getting a cheaper larger-pixel device until Cubase is properly adapted to fully scaled operation, which may not happen all that quickly, just because it will only generally benefit from ubiquitous cheap super high-res displays.
While it is not really a problem for DAW work, the P2815Q is limited to 30Hz@4K. It appears to be becoming unavailable. It was always going to be an interim solution.