That's interesting, I have a worse CPU than you but mine doesn't hit over 20% and that's with other stuff open. Also, Opera does support the game, just not the sound. I played on both Opera and Chrome and never encountered an issue, the game worked perfectly and never spiked anything. I'd love to tackle it but I literally cannot replicate it so I don't know what to do. This is my first game and first time using GDevelop. I'll try to look into it for future updates even though I can't figure out why it's happening. The game isn't very big in the first place, so even being unoptimized it shouldn't be failing so badly.
Glad you liked the parts not affected by the optimization issue.