Several options... Depending on how complex the configs are. Up to and including taking the partial configs and doing a load merge on them.
Last time I did this, I created the new objects via tmsh which was built from the output of 'show ltm virtual' and 'show ltm pool' (I had a lot of mixup to do to bring everything into standards for naming etc at the time, so a simple migration wasn't really an option).
Most iRules and profiles pretty much went as new. As it was also an upgrade from 10.2 to 11.2 at the time...
How many VS's and pools do you have? And how many BigIP's? For a huge number, I'd probably try & get the old box to the same version (Making a merge easier), or write a script to parse the old config and produce tmsh commands to create the config.
H