If you're using wifi on your PS4, check the connection strength. If it's not very strong, then your speed is going to be affected. Use an ethernet cable. This will at least give you the best possible connection.
Second, your internet speed that your ISP quotes you is its theoretical maximum when connecting to your ISP's server. You will NEVER see speeds that fast in real life when connecting to other servers on the internet.
Third, PSN is intentionally throttled (think of it as a speed limit.) This is to prevent a few users with very very very fast connections from starving out everyone else with a slower connection. By fixing the maximum speed to something lower, more people can get a good connection whether they're downloading a game, or trying to play online.
The speed tends to go up a little bit late at night when there aren't as many users online, so it probably won't take 40 hours to download your game, but it's going to take a while nonetheless. After all, you're trying to download nearly 60GB. That's the equivalent of almost 30 hours of HD streaming video.