Is my treehouse platform structurally sound?
Just notes:

2x6s... plenty big.   Weight is a factor unless you will reinforce more.   You do not want it too heavy and these trees aren't that big.

see no issue with having boards a couple inches from trees.   As commented you can always re-evaluate and cut/sister these in 10 years.   Having a tree house means your structure needs to move with the tree(s).

you do need cross bracing

I don't see a a good way to get IN the treehouse.   Is the plan really to climb 15 feet then turn your shoulders so you can squeeze through 14&quot;?

really the only thing I don't like is the resting on the bolts.   I am not against this method but I would like to see an &quot;eye&quot; or a &quot;C/D&quot; anchor that holds these into place (installed underneath).   It doesn't have to lock but I think your current design flaw is this thing rolling to one side.