I think you may have selective memory with regards to VS6 (understandable over 15 years). Having recently worked at a company that for silly reasons did not upgrade beyond VS6, it was not lightning fast, took several minutes to open, and crashed frequently even with smaller projects.

Modern VS really needs to work on managing large projects- but this isn't something it ever had to begin with, and has certainly improved since VS6 despite added functionality. The responsiveness issues you list seem a little more problematic than normal from my experiences- I would definitely try uninstalling a few plugins and seeing if that helps.