Just scale it down to 1080px height and save it as a jpeg with 75% quality. Nobody will ever see the difference. Most browser windows will never display that picture bigger anyways (that means you can use computationally more expensive downscaling offline vs realtime downscaling by the browser).

I wouldn't vectorize it, that would have you lose the hand-drawn feel of it.

Given its graphic nature I would vectorize it. You can compress it more if you clean it up in PS first.

https://vectorizer.ai/images/1695712791489-52152002c3989318-...