I haven't upgraded to 15 yet since there's still one major feature I really need, and that is the ability to save plug-in chains as presets. For example, I might want to save a preset for a particular combination of plug-ins, each with specific parameter settings, and then save another preset of different plug-in chain and settings. This is very useful if I have multiple headphones and monitor speakers, and I have specific EQ, crossfeed, multiband compressions...etc settings for each of them, and when I switch between them quickly to compare them, I would need instant switching between entire plugin-in chains/settings with a single click. This is also very helpful when I have room correction and EQ correction and crossfeed settings for the monitors and headphones, and I want to be able to turn entire plug-in chains on or off instantly instead of clicking on them one-by-one which take too long for quick A/B comparisons. It's also very important to force some plug-ins to remember settings. Something like Easy-Q can save presets, but does not automatically recall them, and it would be crucial to force plug-ins to recall settings for various plug-in chains.
If this feature gets implemented, I'll upgrade for sure.