If the remote sites are trying to access something which resides on the central site (where the controller resides) there shouldn't be too much of a performance hit.
But since campus APs per default are tunneled back to the controller before the client traffic truly enters the network .. it might seriously hinder performance, depending on bandwidth and or latency (in both directions) when they try acessing resources on their own site.
So make sure your bandwdth is sufficient in both directions.
No much else to say about this config.. just test and see where the bottleneck resides.
If you think the ipsec/gre is adding too much overhead (it shouldn't) just configure an AP to bridge the traffic locally and test again.