[solved] I eventually deleted the entire build directory and recreated it (CMake based). That resolved the problem. devenv.exe is sitting comfortably at 460 Mb now, and <1% CPU load.
First, I deleted the .SDF and .DB files (MS switched to the .DB format in Update 2 I think). Didn't help by itself. VS bounced to 2Gb+ and ran out of memory: http://imgur.com/ncRwpqE :-)
License: --------.dk (25-user license) Support ends 2016.03.03
Trial extension mode
VA_X.dll file version 10.9.2094.0 built 2016.03.25
DevEnv.exe version 14.0.25123.0 Professional
msenv.dll version 14.0.25123.0
Comctl32.dll version 6.10.10586.0
Windows 10 10.0 Build 10586
8 processors (x86-64, WOW64)
Language info: 1252, 0x406
Platform: Project defined
Stable Includes:
C:\Program Files (x86)\Windows Kits\8.1\Include\winrt;
C:\Program Files (x86)\Windows Kits\8.1\Include\shared;
C:\Program Files (x86)\Windows Kits\8.1\Include\um;
C:\Program Files (x86)\Windows Kits\10\Include\10.0.10240.0\ucrt;
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\atlmfc\include;
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include;
Other Includes:
Stable Source Directories:
C:\Program Files (x86)\Windows Kits\10\Source\10.0.10240.0\ucrt;
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\crt\src;
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\atlmfc\src\atl;
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\atlmfc\src\mfcm;
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\atlmfc\src\mfc;