That's a lot of .jpegs. I don't know why it would be sluggish, but of course yours are probably very high resolution images. You would be better off asking a professional photographer. Fortunately we have many of them participating on this site.
From the description of your needs, it seems to me that I would use the Photos app before attempting to shoehorn Preview into that kind of service. Preview is very broad-based and not ideally suited for that specific a task. I suggest posting your question in the Photos for Mac forum. Photos might not do what you want either, but you are certain to find more qualified opinions from one of that forum's more experienced participants.