I just had a 80 mph rated roof installed 2 years ago. After this last storm some tiles broke off because of the wind. I want to now have a 115 mph roof installed. Should I just install the new roof over the existing 80 mph roof or have the whole roof re-done? I plan on living here for many years.

Some municipalities allow you to set one roof on top of another some don't.

Also check your home owners insurance and warranty of the new roofing to see if either are voided with the second layer.

Personally if you ever have a leak it may be more easily repaired with a single layer.

That said there is cost in removing the old roof.