Venture theme (depending on how old your version is) doesn't have settings to disable the images but you could edit the code to remove them. One option would be to use CSS to mask them, but the code will still remain. Some browsers will also still download the images so this won't be ideal if you're looking to remove for loading speed.
Are you open to editing your Liquid files in the theme? The file you'll want to look at is /snippets/site-nav.liquid. Should only be a line of code but want to gauge comfort levels first before diving in.
I have stumbled across this thread, as I am having the exact same issue.
I would like to remove the preview of thumbnails in the dropdown menu of the venture theme. Mainly I would like to do this since I am building a log-in only with custamized pricing depending on the customer (b2b shop). And the dropdown menu displays prices before the customer even logs in.
The best solution would be to remove the display of products in the drop down menu all together.
I would also be fine with editing the CSS code as suggested above. Perhaps you could advise in more detail as to how to do this, since I am not the most tech savvy.