to upgrade to the metal table, you need to call weber
technically they should not sell you one unless you own a 2015 performer.
you may get lucky and get a CSR that will let you buy one.
or you may need to register a 2015 performer first (which will require a serial number)
Some have called and been able to order without much hassle.
Others have had to go to Lowes to get a serial number to register.