A 1.5 mb picture taken from a camera will be very close to a 5mb picture. If you have good looking pictures on a full screen nice resolution monitor the difference isn't gonna be anything you notice going from 1.5 to 5... The real differences is when your taking RAW pictures which are like 50-100MB each and need to be processed in something like photoshop before they even look correct. My friend is a photographer and shows me some of his work. He spends a good hour or more on each picture he takes from RAW state to finished jpeg.
Regarding RAW files, the size is limited by the original capacity of the camera you are using to shoot the image. My Sony DSLR shoots 24Megapixel images in the RAW mode. The primary difference between the RAW and JPG images is that the RAW file is lossless and has ALL the information as shot, where a JPG is a compressed file and there are pixels lost with each level of reduction in the size of the image.
The majority of the current DSLRs shoot about that size RAW file. 50-100MP files are reserved for the really high end cameras which most of us can't afford.
A RAW file can be converted to a JPG with a few mouse clicks. What the photographer wants as a final image determines the amount of time they are willing to spend to accomplish that.
I've been a photographer for more than fifty years and when digital came along I jumped in with both feet, stopped shooting film and have never looked back.