You need to answer that question. How big are your paintings. If they are on the small side the cheaper machine may serve you well. What you need depends one what you want to do. Small load or heavy load. How many application will you have open at a time etc. Try to use the machine before you buy. Pay attention to the display. You may want a model that has a larger low resolution display rather thne a small display with high resolution,
Consider "future proofing" and buy it so that you won't be replacing it sooner as new editions of Photoshop and windows taxes resources. Saving money is wise, buying twice isn't.
But anyway check out some reviews: Inspiron 15 Inch 7573 - YouTube
I need a new laptop in order to work on my graphic novel. My old laptop is starting to wear out and does not work well with the new Photoshop CC. I have owned a dell Laptop Inspiron 15R-5521 with an Intel Core i7 3rd Gen 3537U and 8 GB of Memory since 2013.
A simple answer to your question is that you need to purchase a laptop that has higher-performance components than your current laptop. How do you do that? Go to the PassMark website below, which has a tool for comparing your current CPU and GPU with the new model laptop you are considering. As JJMack mentions a higher-resolution display puts even further demands on the system. For this reason a 1920x1080 display is a better choice than a 4K display. Here's an example comparison of the CPU in your current laptop and the one you're considering, which has about 2x the performance.
You'll need to compare the graphics processor for both at Passmark, which I suggest has 2x performance as a minimum. I also suggest 12 GB memory as a minimum. The Dell Inspiron 15 7573 laptop looks like it will meet these "minimum requirements" and the overall performance should be 1.5 to 2 times better than your current laptop, but that's about all. If you're looking for more improvement you'll need to get a laptop with higher specs.
I use a Dell XPS 15 (9550) that I am pleased with. The touch and wide gamut display are unwanted and make colour management more complicated. But the performance is pretty good. I use my laptop only for graphics work. The high res screen is not a problem. I have 32GB ram and internal and external ssds.