The result of the file

    kernel-build-times-20-iterations.txt

is obtained after running

    $ for i in {1..20}; do make clean; \
      time make -j 3; done 2>&1 | tee  \
      defconfig-make-output-20-iterations-l2.txt

in L2 (nested guest).

And, then running:

    $ cat defconfig-make-output-20-iterations-l2.txt \
      grep -i bzImage -A | tee \
      kernel-build-times-20-iterations.txt