I think the game will sell 15M pretty easily. The people trying to downplay the significance of Spider-Man were clearly off their rockers. He's up there with Mickey Mouse and Mario as one of the most recognizable characters in the world. Activision badly wasted the potential of the character while they had the publishing rights.
I think you're off your rocker.
Logic and data say you're way off the mark.
Spider Man 2 on PS2 gen scores 80+% on Metacritic, sold on the back of the highly acclaimed (best ever) Spider-Man movie, to a multiplatform install base of probably 80 million PS2s (70 million sold as of Jan 2004) and another ten+ million of XBs and GCs. Going by VGChartz (if you've a better source, please provide!), SM2 sold something like 5 million. Maybe to 7% of the console market.
The best selling single player games on PS4 to date haven't even broached 10 million.
Spider-Man is not the strongest super hero IP in the world - Batman has that title. Batman Arkham City, a metascore of over 90%, sold something like 10 million to an install base of 50 million PS360s. Some 20% of the market bought that game.
Insomniac's Spider-Man is a weaker IP than Batman, and is a lower rated game than Batman Arkham City - you'd expect it to sell to a smaller proportion than that game's 20% as ti's weaker in two areas. The previous killer Spider-Man game only sold 5 million units out of a similar install base to PS4's. The PS4 SM is selling to a smaller audience without the same movie-assist - the SM:Homecoming isn't rated as highly. PS4 SM is a bit higher rated though. The better rated, stronger brand Batman game was maybe only just looking at 15 million units if the market had been the same size as PS4's, so how can one predict >15M for a lower rated game on a weaker brand?
There's not one single piece of evidence to suggest Spider-Man can sell 15 million, let alone
pretty easily. If it sells over 10 million, it'll have busted sensible predictions. It may be helped past previous records thanks to game streaming and stuff which previous Spider-Man and Batman games haven't had, but that'd be a wild-card outcome.