Full honesty - I don’t want to be discouraging but if you have to do 10-15h a day of work/study already I think you should probably postpone your Japanese learning and just focus on that.
WaniKani it self requires a good amount of dedication to progress at a decant pace, you can do it slowly but quite frankly you probably aren’t going to get super far or to a place where you can actually utilize what you’ve learned by the time your med-school is over. The only thing that’s gonna happen is your JP study will interfere with your med studies and possibly burn you out (even more) by eating into what little recration time you have.
Another issue is that in addition to using WK to learn kanji and vocab you also need to use other resources outside of WK to learn grammar and other aspects of the language, which you clearly have no time for.
I think you should probably focus on the more imporatant part of your life right now which is likely your med studies. Once you’ve finished that come back to learn Japanese at your own laisure when you have more time to spare, you’ll probably see more and faster progress than since you’ll actually be able to give it enough attention.
Obviously it depends on what kind of person you are and what you’re capable of doing with but putting my self in your shoes this is what I would do.