Yes, I can explain although the answer isn't likely to make you happy.
Please don't shoot the messenger (me).
It has to do with an increased Medicare premium based upon your adjusted gross income in 2014.
Here's the chart that explains the increase.
Your modified adjusted gross income as reported on your IRS tax return from 2 years ago is above a certain amount.
If you're in 1 of these 5 groups, here's what you'll pay:
If your yearly income in 2014:
For individual filing status:
$85,000 or less $121.80
above $85,000 up to $107,000 $170.50
above $107,000 up to $160,000 $243.60
above $160,000 up to $214,000 $316.70
above $214,000 $389.80
For Married Filing Jointly Filing Status:
If your yearly income in 2014
$170,000 or less $121.80
above $170,000 up to $214,000 $170.50
above $214,000 up to $320,000 $243.60
above $320,000 up to $428,000 $316.70
above $428,000 $389.80
So basically you need to check out your 2014 tax return and see where that puts you on the chart.
In 2015 you probably were at the $121.80 premium level (per person)