In the gamecard gog says the final game download is 1.3 gigabytes, but the demo is 2 gigabytes.

Are you sure, Gog?

No thats a place holder amount. The actual game will be around 15 Gigs

The filesize was what kept me from buying the game, an HD FMV game that small had to be short

The filesize represents the size of the demo, which is just one location.
It was verified by Cubase (who is in charge of all the FMV in the game) that the full game will be about 15GB download.

So go ahead and buy it ;)

I just did xD

actually the size 1.3gb was the beta size that was placed on gog first & then the demo was loaded & gog didn't change the download size to 2.3gb. the game is a whopping 15gb

Thanks for clearing this up guys, I've been thinking about pre-ordering this as my first Tex Murphy game, and I was really hesitant comparing the size of this to the older games.

They should change the file size on GOG info page as it's not accurate at all.

I agree with you. This topic has been brought up for weeks now, dozens of people asking why the game size is only 1.3 GB. I don't understand why GOG just changes the download size to the estimated 15 GB on the game site. Reading that people didn't pre-order the game because of this I think it actually might have hurt the sale.
Well, the release is in a few days, so it's too late for it now I seems.

Steam says the storage requirement for the game is ~15GB. I expect it to be bigger than even that.

I haven't seen the actual interview, but Wikipedia cites that Tesla Effect is about twice the size of any of the last recent Tex Murphy games (I'm guessing they're referring to Overseer).