Queue ringall extensions

I’ve got a queue with 3 extensions added and set to ringall. I have another set of 3 extensions that I will be using to connect mobile softphones. I do not want to add the mobile softphones as part of the main ringall. Is there a way to ringall mobile extensions if the main 3 extensions are unanswered after two attempts?

Let say that 2 rings are 15 secs queue time.

You could set a 2nd queue as failover destination, including the 3 mobile extension, so when the 15 secs have passed without no anser in the 1st queue with the main extensions, it will join the 2nd with the mobile ones.