Life Insurance Beneficiary %?

I would like to split my life insurance beneficiary between my wife(85%) and mother(15%). For some reason this discussion really irritates my wife,she thinks she should get 100%. I'm not splitting it to be a jerk, I would just like to leave something for my parents so they could take care of their bills or medical needs. If I die of Natural causes my job would pay $50,000.+ supplemental life of about $288,000.= $338,000.- $50,700.(to parent) would leave $287,300. for my wife to cover funeral,payoff $77,000. mortgage,and live a normal life taking care of son. Let's not even mention accidental death which could get up to 800,000. I always joke with my wife that's to much money for you to be spending on the next man:-).What would be a good way to explain this to my wife?