It's tough to say since you don't give us much information to work off of. What are you studying in college? What tasks do you need the laptop to do? How important is gaming to you? What sort of battery life do you need?
Based on "slim and powerful with a 15ish inch screen" and the $2000 budget (which is a lot), I'd say look at the Dell XPS 15 and HP Spectre x360 15. They are both around the weight of the 15" MBP (4.2 - 4.4 lbs), about 1-2 pounds lighter than most 15.6" laptops (the MBP is 15.4").
http/www.notebookcheck.net/Dell-XPS-15-9550-Core-i7-FHD-Notebook-Review.158875.0.html
http
/www.notebookcheck.net/HP-Spectre-x360-15-ap011dx-Convertible-Review.159134.0.html
For "powerful" you should get a quad core (probably i7, but there are now i5 quads for laptops). But be aware that they put a serious dent in battery life. The MBP and XPS 15 manage to get decent battery life from a quad core by including massive 90+ Wh batteries. Most 15" laptops with a "normal" battery (around 40-50 Wh) will only get about 4-5 hours battery life with a quad core.
4k resolution isn't as important on PCs as it is on a Mac. Windows uses subpixel rendering for fonts (called ClearType). That essentially triples the horizontal resolution, so a 1920x1080 screen acts more like a 5760x1080 screen.
https/www.grc.com/ctwhat.htm
The higher resolutions are more important on a Mac because OS X doesn't do subpixel rendering. One of the core markets for the Macs are page layout artists. They need to know *exactly* what the text on a page will look like before it's printed. Subpixel rendering will shift fonts slightly left or right to line them up with the subpixels. That's unacceptable for professional layout work so Apple opted to use more precise (but blurrier) font anti-aliasing. As a result, the only way to improve the appearance of fonts on a Mac is to use a higher resolution screen.
So generally I recommend going with a 1080p screen on a PC laptop. The exception would be if you do extensive graphics work like Photoshop. The extra resolution can help there (can view a larger photo at native resolution, without needing to rescale it for the screen resolution). Or if you do a lot of programming and your eyes are good enough to read tiny fonts. Programmers generally like being able to see lots of code at once.