The game goes on for over 100 hours after C3, that 15 you spend learning is not even a blink compared to whats coming, the depth in the game is so high it has to spend the first 3 chapters making you aware of what you can do it's geared for players who are in it for a long game. If you're not pass chapter 3 you've not started the game at all.
Im well aware its a long ass game but still 15-20 hours before the "real game" starts is excessive.
Xenoblade X, Breath of the Wild & Skyrim are a couple of games in the last few years that i have or am on track to putting 70+ hours in and it didnt take anywhere near 15 hours for me to be engrossed in them.
I just double checked to see where i left off since i havent played for a few weeks, i was actually midway through chapter 3 so ill take your word for it and try playing again once im done with Skyrim.
When the herd loses its way, the shepard must kill the bull that leads them astray.