Ideas for taking druid multiclass to 15

[KorvinStarmast]

It sounds like there is a few spells that stand out but no automatically great spells so thinking more levels of either Monk or cleric might be of more benefit than the access to 6 level spells? Although it's hard to think of any one subclass and it's third level features being better than access to 6 level spells and a couple more slots (in the case of monk) or access to lower level cleric spells (that continue slot progression)

It's certainly interesting to think of options!

Heroes Feast is really good.

The four investure? Not so much.
Wind Walk is IMO a 'must pick' unless you do no traveling in your campaign.