After Visual Studio 2008, they rewrote the UI in WPF and started writing large components of the program in C#. This dramatically regressed performance, especially on a cold start (it runs decently if you've had the program open for a while). I'd probably still be using Visual Studio 2008, except it limits you to C89 and C++03.
C# is working hard to be Rust-like in certain areas of performance. Part of Visual Studio's problem is that they can't yet take advantage of it in some key areas because they are still dependent on the Legacy Framework and Legacy WPF and have to migrate to modern .NET.
Cold boot perf is a good yard stick but it’s not that important in your workflow. Except when it crashes. They really should work on that. Quality as a feature.
I don't understand how the editor has regressed to the point that 15 year old software performs better than the modern equivalent.