Hey, your issue is with the RPG Maker MV tileset size, not with the single tile size.
Here they are:
A1 and A2 are 768 x 576 pixels
A3 is 768 x 384 pixels
A4 is 768 x 720 pixels
A5 is 384 x 768 pixels
B-E Tilesets are 768 x 768 pixels.
You need to resize them in order to fit in the given size. If you need help doing that, comment again :)