According to the 2005 budget request, linked from
this page, the OPM requested just over $35 billion in FY 2005. [15% of this represents $5.25 billion].
According to the breakdown, just short of $34.5 billion of this is "Mandatory Spending" and appears to relate to pensions, health insurance and life insurance for all (civil) federal employees.
Whilst we have trimmed the size of the federal government, and therefore inevitably the number of employees in it, I honestly doubt we've trimmed 15% of the federal workforce. Unless there has been a similar reduction in employee numbers, this cut will largely be paid for by cutting into spending on employee benefits.
I have little experience of federal employee benefits, but I presume that employees either have to, or have the option to, contribute towards their pensions and other insurance. If this isn't the case, I wouldn't mind a clarification.
Given that health insurance is going to cost as much as its going to cost (I am not going to ask the OPM to haggle with hospitals over how much they will charge for emergency surgery before an employee gets it) and life insurance is a mere $35 million, the vast majority of the cuts will come from the pensions & disability benefits. Given that employees may have invested in these themselves, and were also to an extent probably relying on it for their retirement, I think cutting it would be highly irresponsible.
Whilst I would be willing to investigate reducing costs of benefits for
new employees, this will not do anything to the budget short-term, and it will be a good decade or two before any improvement is really seen.