Its easy to confuse DPI and PPI. The first is an output value for a particular printer, typically 720 for inkjet printers but high end laser printers can have a much higher output value.
On the other hand pixels per inch refers to the input value of a digital image, typically 72 to send to a PC monitor or between 240-300 to send to a printer. The ppi value won’t change the original pixel size of an image, it will simply affect the maximum size that can be printed on paper. In your case a 24mb file with larger pixel dimensions would be capable of producing a larger size print at a given ppi value, subject to printer limitations, but the quality from the printer should be the same.
The real advantage of a 24mb file is in creative cropping to improve the composition. Quite a large area can be cropped and you are still left with a very usable photo.
See this wiki for further information: