Standby comes up with old configs

I would try a couple of things. Look in the logs and see if ConfigSync is failing. I'd expect that it is. If you can get them to sync, that's always best. Barring that, I'd get the "good" config over to the standby box using an SCF or migrating bigip.conf, or something. Then once you have all that working, I would upgrade to version 10.2.4, and then I would talk about upgrading the 1500's as they went End of Sale in 2009, and End of Software Development 8/1/2012. :-)