We migrated a PB 12.5 application to PB15. No issues. Then we compiled the app using the new 64 bit option.
Again we used the PB12.5 RTC files for the deployment.
We deployed the app to a Windows 8 machine and started testing. As stated in the documentation, the RTE control does have a different appearance in the 64bit environment but we are not supposed to test this anyway. Also, for some reason the Help files will not open from within the application. Other than that, no issues yet.
We are testing with the 64 bit SQLAnywhere and the 64 bit MSSQL drivers. No problems yet.