Hugo is of course using GIT and GO. And you can use both of them to your advantage. First GIT: to checkout v15, you use this command:
$ cd hugo
$ git describe --tags
v0.15-428-gbfe8009
$ git checkout -b local v0.15
Switched to a new branch 'local'
$ git describe --tags
v0.15
And once this is done, you can compile like this with GO:
$ go build -o ~/bin/hugo main.go
This method works, but it has one caveat: the packages in $GOPATH/src/ stay as they are, e.g. they aren’t rewound to what has been used when the original hugo v0.15 has been built. That said: building worked, and running this hugo worked, too.