Not for me (on Windows 10).
Do you select the "Open anyway" option in the spurious ACR version warning, or "Render using Lightroom"? If the latter, yes it will be slow. The one to choose is "Open anyway".
If you've chosen "Render using Lightroom" and told it to suppress the warning, you can get it back (so you can choose the other option) by Preferences -> General tab and click "Reset all warning dialogs".