I assume any new FMP15 calculation functions...is there anything else?
Or, for more detailed explanation, check the new features chapter here:
Here is all things that is new in FM15
Essentials for unique custom apps | FileMaker 15 Platform
You should build a script that you have on OnFirstWindowOpen script trigger that check if your version is FM15. If not, give use a dialog that they need to install FM15 before they can run your solution
For example, the Truncate Table script step.
Also, look at this
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