Hello, your island is pretty nice but will need some more work before a proper review is done.
Sheogorad doesn't use the Sand texture, only Sand_02
There are lots of texture seams, these need to be cleared or covered. It can be helpful to look for them with objects hidden (shift-c)
There is a lot of stretched or jagged terrain that needs to be smoothed.
The wilderness is underdetailed, use more container flora
At a quick glance I also noticed the following issues:

4,30
-A menhir is rotated in its side, showing the see through bottom
-A mushroom tree has its cap bleeding into a rock
-A mushroom tree is inside of a rock
-That same rock needs more vertex shading

5,30
-A menhir is bleeding into an emperor parasol cap
-An AC mushroom tree cap is bleeding into an emperor parasol cap
-Weird floating small emperor parasol in the south is both bleeding into the top tree and bottom roots, while the bottom of the tree caspers through the roots.

6,30
-Town layout is nice, but missing clutter. Add crates and barrels.

4,29
-Needs more underwater detailing

5,29
-Tree inside of a rock
-Kreshweed inside of a rock
-Many trees growing out of rocks in the north
-Mushroom tree cap bleeding into emperor parasol

Once all this is taken care of I will do a more in depth review of this showcase.