Bootcamp + Windows 8.1 + Apple Macbook 2011

SSD might do it - that's what I'm guessing is the difference between your boot time of 1:30, which is about right for an HD boot drive, compared to 5s, which is fast even for an SSD [I'd suspect it was hibernating rather than booting to be quite that fast]

More RAM would also help a lot - 4GB is bare minimum for a modern 64-bit OS, 8 is more acceptable, 16 would be nice. Your lack of RAM will be what is causing Visual Studio to be paging to the hard drive, at a guess, & causing the slowdown.

I can say it's not memory. I have a new MBP since 1 week, with a SSD under WIN64 8.1 and 16 GB of memory and exactly the same behavior, instead maybe it's not permanently, maybe 100 % during 10 s every 5 or 10 minutes.