The primary differences between an intravehicular suit and an extravehicular suit have to do with (1) how well the pressure bladder is constrained against ballooning (so that the wearer can actually do useful work), (2) whether the insulation and heat-management systems are good enough to keep the wearer from broiling in the sun and freezing in the shade, and (3) the amount of radiation and micrometeoroid shielding provided in the outer layers. None of these things are relevant to mere survival in a depressurized spacecraft
A Mercury (i.e., modified Navy Mark IV) suit is designed to hold 3.7 PSI. The same is true of the Gemini G3C through G5C suits, and the Apollo A7L and A7LB suits. The Soviet Vostok (SK-1) suit was designed to hold 3.9 to 4.4 PSI, the ACES 3.5 PSI, and the EMU 4.3 PSI. Of these, only the Apollo suits and the EMU are extravehicular suits.
A Russian Sokol suit, though strictly an intravehicular suit in terms of ballooning management, thermal management, and shielding, is designed to hold 5.8 PSI.
But what difference does any of this quibbling over how long a human being in a Sokol suit survive total cabin depressurization make, if the reader's first impression of the protagonist is so bad as to encourage complete apathy as to whether he lives or dies, and the antagonists are portrayed as stereotypical caricatures with no motivation beyond pure sadistic malice?
Going back to my first complaint about the book, I freely admit that I've been guilty in my own writings of making a protagonist totally unsympathetic, by bungling "protagonist kisses baby" passages so badly that the average reader see them as "protagonist kicks dog." But Gillebaard doesn't even appear to have been trying to make his protagonist sympathetic.