Generally, external monitors are better than laptop screens. Laptop screens prioritize weight, thinness, and power consumption. Image quality is often sacrificed. For example, most laptop screens hit between 60%-80% sRGB color space (color gamut, or maximum saturation). Nearly all external monitors are designed for 100% sRGB.
https://pcmonitors.info/reviews/dell-s2415h/
Reviews of the S2415h are favorable. If the image is not very crisp, make sure the video card is in full color gamut mode. And make sure it is not overscanning (enlarging the picture being sent so it's slightly bigger than the screen).
https://pcmonitors.info/articles/correcting-hdmi-colour-on-nvidia-and-amd-gpus/
IPS is not a setting. It's a different way of arranging the LCD which controls which pixels are lit, which allows the same color and brightness over a wider range of viewing angles. It is always "on". If you stand above the laptop and monitor and look at the screens from that elevated angle, you will probably see the laptop screen's colors have shifted, while the IPS monitor still looks good. That is what IPS (and it's equivalent from other manufacturers) gets you.