For us, the #1 biggest problem in FileMaker 15 -- which makes it unusable for some of our solutions -- is that we can no longer filter the script list by folder within the Script Workspace.
We have created some FileMaker solutions with thousands of scripts in them, and the only way to organize thousands of scripts is to carefully organize those scripts into extremely carefully-named folders. In FileMaker 13 and every version prior to FileMaker 13, we could easily show just one particular folder's worth of scripts. But this functionality was inexplicably removed from FileMaker 14, and for some reason, it still hasn't been brought back to FileMaker 15 yet.
In fact, filtering the script list by folder is STILL AVAILABLE throughout ALL THE REST of FileMaker Pro! For example, if you are writing a script and you choose the "Perform Script" script step, that script step ACTUALLY LETS YOU FILTER YOUR SCRIPTS BY FOLDERS! See screenshot below.
The screenshot below is a FileMaker 15 screenshot. Every single area of FileMaker 15 gives us the ability to filter scripts by folder... except for one place. The #1 most important place where we need it... the Script Workspace.