I\'m working on a ColdFusion project for a while now, and Visual Studio started to behave strange for me at least.
I observed that when I started debugging, it built
Debug -> Delete All Breakpoints ( http://darrinbishop.com/blog/2010/06/sharepoint-2010-hangs-after-visual-studio-2010-f5-debugging ) After that you can use them again, but do it once. It will remove some kind of "invalid" breakpoints too and then loading symbols will be fast again. I was chasing this issue for days :(.
I faced a similar problem. In my case I had set _NT_SYMBOL_PATH to download from Microsoft Servers for use in WinDbg and it looks like when set, Visual Studio will use that with no way to ignore it. Removing that environment variable resolved my issue.
Visual Studio 2017 Debug symbol "speed-up" options, assuming you haven't gone crazy on option-customization already:
Tools -> Options -> Debugging -> Symbols
C:\dbg_symbols
or %USERPROFILE%\dbg_symbols
1A and 2 are the most important steps. 1B and 1C are just helpful changes to help you keep track of your symbols.
After your app has loaded all the symbols at least once and debugging didn't prematurely terminate, those symbols should be quickly loaded the next time debug runs.
I've noticed that if I cancel a debug-run, I have to reload those symbols, as I'm guessing they're "cleaned" up if newly introduced and suddenly cancelled. I understand the core rationale for that kind of flow, but in this case it seems poorly thought out.
I had the same problem and even after turning the symbol loading off, the module loading in Visual Studio was terribly slow.
The solution was to turn off the antivirus software (in my case NOD32) or better yet, to add exceptions to it so that it ignores the paths from which your process is loading assemblies (in my case it is the GAC folder and the Temporary ASP.NET Files folder).