You really should have stopped wasting money a long time ago.
Literal
Wasteful-spending [topic-は] long-ago stop-[progressive-ていて] good stage [copula-だ].
とっくに ('long ago, ages ago') is a casual adverb. やめていてよい = 'would be fine to have stopped [already].' ころだ ('it's time/stage [that]') marks a temporal expectation. Literally 'it's the stage where it would be good that [you] had already stopped wasting money.' Reproach for procrastinated behavior change.