Whether you do the work now or do the work later, you pay the price. If I may offer a suggestion - it costs less to pay the price now, before years of deeply engrained bad habits must be corrected.
If your teacher asks you to do something, do it. Not just for a day, or a week, or a semester. These are things you will do from this point forward until you lay the horn down for good. You will never reach a place where long tones, lip slurs, and scales are optional! If the lip slurs get easier, add a partial, change a tempo, or otherwise expand your frontiers. Practice goals aren't boxes to check off of a list - they are daily tasks which must be done thoughtfully and diligently to thrive as a performer.
Anyone can say that they "want it," but the ones who "do it" are the ones who will make it.
Will you be a wanter, or a do-er?