Opus doesn't access .svn folders directly, so it'll be TSVN which is doing it, possibly to generate the icon overlays showing SVN status.
Turning on Show generic icons for... and/or turning off Show shortcut arrows and other icon overlays in the same Preferences page may stop that happening, but would affect other folders as well. Blocking the TSVN icon overlay shell extension (e.g. via ShellExView) should prevent it from being invoked entirely without needing to change anything else.
For a proper solution, reporting the issue to the TSVN devs is probably the best bet.
The thing that takes time is the thing that needs to be addressed. That's in TSVN, so it's something you likely need to bring up with the TSVN developers.
Although if TSVN is still being queried when the overlay is disabled and the columns are not turned on, then something must still be triggering that. Maybe you've set up labels or something else that tests TSVN state to color files or similar? That could also explain why File Explorer isn't triggering it, as it can't do that.