Nintendo will announce official sell in figures on February 2nd.
In the mean time we can use data from The NPD Group and Media Create to compare Wii U sell through for the USA and Japan.
In the USA sales were down approximately 13.5% YOY according to the NPD Group.
In Japan sales were up 42% YOY according to Media Create.
However the absolute unit difference in these two territories was only around +50,000 units in 2015 compared to 2014.