I have this issue in VS2015 but not in VS2013.
In vs 2015 I was able to improve things by turning off
tools, options >> text editor >> C#, Advanced and uncheck Enable full solution analysis.
But there is no such option in VS2013
Interestingly in my VS2013 any x:Name values are not available in intellisense until I have compiled once. I have no idea why (I must have set some setting at some point in the past but I don't know what), but it make the tool at least usable.
I have also found that keeping the number of tabs open to a bare minimum really helps, and closing XAML tabs whenerver possible also makes a big difference.
This really should be near the top of the bug fixes IMO. Many potential users encountering this issue may stop using the tool and never come back.