It's hard to give these numbers their appropriate weight, really. Five times worse than a place where a 13 year old is more likely to have been raped multiple times than know how to read? Five times worse than a place where ritualistic murder and cannibalism is still practiced? Five times worse than a place where the police extort protection money through torture and murder? What does that place even look like?
OK, a few points you've overlooked.
1) 'Society' doesn't mean that the world suddenly gets nicer to you. In fact, in many ways, it just finds new ways to screw you than just 'survival of the fittest'.
2) Don't forget disease, malnutrition, and wild paracritter attacks in those mortality rates.
3) The orks stay in places like the Barrens or the Underground because at least then the predators they face (both critters and metahuman) don't include the police discriminating against them because of their metatype or lack of SIN.
4) Walls aren't necessary to keep the orks and other SINless in certain areas. When the police catch them, they will typically take their stuff, beat them, and toss them back where they came from, if they're lucky. And walking onto extraterritorial grounds can get you shot.
5) And in the places you mentioned, they don't have a very efficient, wide spread organlegging operation like Tamanous, ghouls and other Infected that have to feed on metahumans in order to survive, rats the size of dobermans, toxic spirits, bug spirits, trees that eat people... I could go on, but I think I've made my point. Yes, being SINless in a sprawl means things are very, very bad for you, and every day could be your last.
EDIT: Also curious, the SINless Orks you talk about they have no rights right? I'm wondering if some serial killers don't show up just killing Sinless. <.< I mean they have no rights you can do whatever you want to them right? That's how it was described in the law enforcement part of the book, that you could wind up dead. You also get the feeling that almost everyone packs a gun it seems. Though we are focusing on the criminal world of it so no duh.
So would Raping or killing a Sinless really be a crime? What if it's a past time to some people in the world.... i'm rather unsure of this topic..... obviously they have gangs protecting people in places like this but still, i don't think too many people care about them.
SINless do have rights, just limited rights. So yes, killing or raping SINless is a crime. It just isn't a crime that the police are going to put a high priority in investigating until a rich person gets involved. Which is why, when Bull's daughter was killed by the copycat Mayan Cutter, he got runners to track the guy down.
What bugs me is that Orks are definitively tougher, so why do they have a higher mortality rate?
Because Orks tend to live in nastier places, with worse medical care, than people of other metatypes.