Watching TV Forensic Files. One guys kills his wife and gets 15 years. Other killers get life without chance of parole. Whats up with that?

The degrees to which the charges of murder or manslaughter are assigned are generally determined by the intent of the offender. Any evidence of forethought, planning or conspiracy constitutes premeditation and merits a higher degree and thus more time.

Crimes of passion occurring spontaneously or in the heat of the moment, generally, are given lesser degrees of murder.

Killing someone with no intent to do so, either by negligence or accident is usually determined to be "manslaughter."

Well, no it isn't. There's manslaughter of various degrees, there's murder of various degrees. All of them made up by some arbitrary formulas made by cigar smokers in some back room.

there are always different levels of crime under the law, it is possible for someone to get a suspended sentence for murder.

It often depends on the lawyer.