Thank you for reaching out and posting this question!
The Fashionopolism is a premium theme and since you've been using them for three years, then we'd recommend taking a look at their latest version of their theme for any new features that may be beneficial for your store. However, if you're looking for a theme that is optimized for performance, then we'd recommend taking a look at our minimalistic theme - Dawn (free). On that note, changing themes will not impact your Google rankings as the rankings is associated with your domain name.
That being said, there are many factors that can impact the performance of your store, and we'd recommend taking a look at some of the factors that you can control from our guide - Improving your online store speed.
I'd love to hear more about your business! Aside from furnitures, do you sell any other types of products? Also, do you have a marketing plan prepared for your store?
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