I have a collection of around 150 DLLs. Over time, due to the different compilers being used, their sizes have steadily, but somewhat gradually increased.

The average size of these DLLs was ~ 11,000 KB when built using D11. When I build the identical DLL projects (nothing gets changed but the compiler), they now all come in at ~22,000 KB.

That's not a gradual increase IMHO - any ideas as to why this might be?