git clone + submodule clone with shallow-clone difference.

README.md

command	clone depth	submodule depth	total sec
--depth + submodule --depth	1	1	125sec
--depth --single-branch + submodule depth	1	1	127sec
--depth --single-branch --recursive	1	1	109sec
--depth + submodule --depth	100	1	126sec
--depth --single-branch + submodule depth	100	1	114sec
--depth --single-branch --recursive	100	100	107sec
--depth + submodule --depth	100	100	102sec
--depth --single-branch + submodule depth	100	100	108sec

depth 1

# shallow: 103sec + 22sec
git clone --depth 1 https://github.com/Org/Repo
cd Repo
git submodule update --init --recursive --recommend-shallow --depth 1 

# shallow_singlebranch: 105sec + 22sec
git clone --depth 1 --single-branch https://github.com/Org/Repo
cd Repo
git submodule update --init --recursive --recommend-shallow --depth 1

# shallow_single_submodule: 109sec
git clone --depth 1 --single-branch --recursive https://github.com/Org/Repo

depth 100 + 1

# shallow: 104sec + 22sec
git clone --depth 100 https://github.com/Org/Repo
cd Repo
git submodule update --init --recursive --recommend-shallow --depth 1

# shallow_singlebranch: 92sec + 22sec
git clone --depth 100 --single-branch https://github.com/Org/Repo
cd Repo
git submodule update --init --recursive --recommend-shallow --depth 1

# shallow_single_submodule: 107sec
git clone --depth 100 --single-branch --recursive https://github.com/Org/Repo

depth 100 + 100

# shallow: 90sec + 12sec
git clone --depth 100 https://github.com/Org/Repo
cd Repo
git submodule update --init --recursive --recommend-shallow --depth 100

# shallow_singlebranch: 96sec + 12sec
git clone --depth 100 --single-branch https://github.com/Org/Repo
cd Repo
git submodule update --init --recursive --recommend-shallow --depth 100