If you use an Apple Silicon (M1) Mac, you will hit an issue when downloading Go 1.15 or earlier via the dl tool.
Here is the solution:
$ GOARCH=amd64; go run golang.org/dl/go1.15@latest download
$ go install golang.org/dl/go1.15@latest
$ go1.15 version
go version go1.15 darwin/amd64