We have several clients that are still on 3CX version 15. It looks like they updated the mobile client today and they are now receiving a message stating that "We have detected an old an unsupported version of 3CX Phone System. This client will not run correctly with this version and will stop working all together on 1/1/2018. Please contact your administrator to upgrade 3CX to v15.5" Why is this message showing? Isn't version 15 still a supported version? Is there a way to turn this off?