To add to the advice above: Look at a set of assets and see what you can share between them. Your grocery store example has a lot of the same shelves and trim pieces that could be reused.
I'd say the main question is how much time you think is reasonable for an asset to take. If your current approach fits within that and allows you to deliver your project on time, then there's not much reason to stress over it. And, going beyond all the techniques possible for individual asset creation, there's also the…