WebView WebAssemly compilation is very slow

WebAssembly is taking forever to be compiled. I've tried Examples/webview/minibrowser, webenginewidgets/simplebrowser, and even built otter browser from sources (using 5.12.3) and any of wasm examples below have same issue. 

Chrome, Edge, Firefox browsers behave correctly btw.

https://s3.eu-west-2.amazonaws.com/wasm-qt-examples/last/index.html

Note: I'm using Windows, not sure if same behavior occurs on other platforms.

Upd: forgot to mention that happens with Debug build, and in Release it's still much slower than other browsers but at least it's not 10-15 minutes