there are detailing requirement for reinforcement, and aluminum bracket that hold the glass in place. And bigfry if you are asking question to a US hobbyist, it helps to do a little metric -> standard conversion for the dimension. 15mm = 2/3" is a little on the thin side. 2000L = 528Gal, 500mmx300mm = 20in x 12 in. the pressure exerted on the glass is less if the glass is located on the top portion of the tank thank it's located on the bottom portion of the tank. remember to post pictures of your tank/pond when it's done. good luck.
Chris