One of the eye catchers of the next gen console, like the PS5, are their SSD’s, which are greatly reducing the loading times of games. It seems, however, that games on the current generations of consoles are also taking advantage of that.
In the run of the release of the PS5 next month many different PS4 games have received an update, most likely in the context of backwards compatibility (making sure the game will work properly on the PS5 as well). A fun side result of these updates is that it seems to greatly improve the game loading times.
In the video given here The Last of Us Remastered is given as a example, before the patch the load time of the game took approximately 90 seconds, after the latest patch of the game was released this was reduced to 14 seconds. The same for the load times of the save files which went to 2 minutes to again 14 seconds.
The exact load times can vary from console, and is also dependable on the HDD you’re using. But it seems certain that the optimizations of the PS5 also have their benefits for PS4 games.