I'd recommend that you contact a VMware partner/reseller, and ask for an offer that contains two options
1.) SnS renewal (reinstatement) for the existing licenses
2.) new licenses including SnS
to see what's less expensive.
Please remember that vSphere 5.5 is already out of support (see https://lifecycle.vmware.com/), just in case that you want to renew support to get help with an existing issue.
André