I tried to install podman on SLES 12 straightforwardly, but it looks like the package is missing.
dmitry@sles12:~> sudo zypper in podman
Refreshing service 'Advanced_Systems_Management_Module_x86_64'.
Refreshing service 'Containers_Module_x86_64'.
Refreshing service 'Legacy_Module_x86_64'.
Refreshing service 'Public_Cloud_Module_x86_64'.
Refreshing service 'SUSE_Linux_Enterprise_Server_x86_64'.
Refreshing service 'Web_and_Scripting_Module_x86_64'.
Loading repository data...
Reading installed packages...
'podman' not found in package names. Trying capabilities.
No provider of 'podman' found.
Resolving package dependencies...
Nothing to do.
The only piece of information I found about running podman on SLES 12 is
SLES 12 is a bad platform to play with current container technology. It's too old for that and build/based around docker, not podman.
source: https://lists.opensuse.org/opensuse-kubic/2019-10/msg00009.html
As far as I know SLES 12 is still supported. I checked the latest release notes of SLES 12 SP4 and SLES 12 SP5, these two were released after the first public release of podman, but there is no any mention of podman.