Play the free version first. It's packed full of content. If you like it and want to support the game and get some more content with it, then decide if you'd like to buy the Premium version.
A lot of games don't compress their images enough, in my opinion. There's no reason that a visual novel should be 10-15GB. I try my best to compress the game into a small file size, while not losing quality.
I know my game has more content than 90% of the AVNs out there that are two or three times the file size.