Um, hold up. You don't think it's your PC? With no dedicated GPU, and an old CPU, seriously? Yeah, this is a 2019 game, it will require 2019 specs to play. No offense but saying "I don't believe it's my PC" when I'm honestly surprised you can even run Classic WC3 on that machine is strange to me.
But besides that the game is currently unoptimized. It only runs on very powerful PCs which I'm sure will not be the case on release (GTX 970 or newer pretty much).
Classic game plays perfectly, the Intel HD graphics 620 is pretty good, it should be placed next to GeForce 920M plus it uses the main memory for storage of which I have 1880Mhz DDR4 so its pretty fast. Anyway, you're right it's optimised so we'll have to wait and see.