to improve performance, which will set the goals
Actually, without the comma you would need to add "the" before "performance", and
then the meaning would
change, specifying which performance you're talking about, i.e. the performance which will set the goals... (and not e.g. the performance which we discussed last month)
As you see, the comma is needed there.
EDIT:
with the comma, the whole sentence after "which" refers to "plan", as it should. Without it, as I showed you above, it refers to "performance"
