Starting Unit Test in Visual Studio very slow, repeatedly loading/unloading same dll

Problem

I'm having serious delays (several minutes) in starting up a Unit Test and it doesn't seem to matter if I'm debugging or not.

When debugging I can see in the output window there is one package that is repeatedly being loaded and unloaded again. This happens literally thousands of times.

'vstest.executionengine.x86.exe' (CLR v4.0.30319: Domain 929): Loaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_32\mscorlib\v4.0_4.0.0.0__b77a5c561934e089\mscorlib.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Loaded 'C:\WINDOWS\assembly\GAC_MSIL\Microsoft.VisualStudio.QualityTools.Tips.UnitTest.AssemblyResolver\12.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualStudio.QualityTools.Tips.UnitTest.AssemblyResolver.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Loaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Core\v4.0_4.0.0.0__b77a5c561934e089\System.Core.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Loaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System\v4.0_4.0.0.0__b77a5c561934e089\System.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Loaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Configuration\v4.0_4.0.0.0__b03f5f7f11d50a3a\System.Configuration.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Loaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Xml\v4.0_4.0.0.0__b77a5c561934e089\System.Xml.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Loaded 'C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE\PrivateAssemblies\Microsoft.VisualStudio.TeamSystem.Licensing.dll'. Symbols loaded.
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Loaded 'C:\WINDOWS\assembly\GAC_MSIL\Microsoft.VisualStudio.QualityTools.Common\12.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualStudio.QualityTools.Common.dll'. Symbols loaded.

'vstest.executionengine.x86.exe' (CLR v4.0.30319: Domain 929): Unloaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_32\mscorlib\v4.0_4.0.0.0__b77a5c561934e089\mscorlib.dll'
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Unloaded 'C:\WINDOWS\assembly\GAC_MSIL\Microsoft.VisualStudio.QualityTools.Tips.UnitTest.AssemblyResolver\12.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualStudio.QualityTools.Tips.UnitTest.AssemblyResolver.dll'
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Unloaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Core\v4.0_4.0.0.0__b77a5c561934e089\System.Core.dll'
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Unloaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System\v4.0_4.0.0.0__b77a5c561934e089\System.dll'
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Unloaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Configuration\v4.0_4.0.0.0__b03f5f7f11d50a3a\System.Configuration.dll'
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Unloaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Xml\v4.0_4.0.0.0__b77a5c561934e089\System.Xml.dll'
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Unloaded 'C:\WINDOWS\assembly\GAC_MSIL\Microsoft.VisualStudio.QualityTools.Common\12.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualStudio.QualityTools.Common.dll'
'vstest.executionengine.x86.exe' (CLR v4.0.30319: Dependency finder domain): Unloaded 'C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE\PrivateAssemblies\Microsoft.VisualStudio.TeamSystem.Licensing.dll'

I tried ...

running Visual Studio 2013 as administrator.

the following solution: http://ift.tt/1PziDFI (Enable Just My Code & Load all Symbols), but when I click the button to load all symbols Visual Studio simply crashes. (sometimes immediately, sometimes after finished loading)

enabling/disabling Microsoft Symbol Servers, which makes no difference.

starting up Visual Studio with logging enabled but there is nothing that seems out of the ordinary or related to my problem.