You won’t find too many fans of the speakers the Japanese electronic titans built during the 70s, outside of the Pioneer HPMs. Personally I haven’t heard that model of Sansui, but I was demoed a similar pair at a vintage shop once and pushed quickly towards other models. I don’t remember it being outright bad, just not as extended or refined / balanced as better 70s speakers.
As for matching / synergy, I’ve been running a bigger brother to your receiver, the SX-750 for over a year now, fully recapped and restored. I find sensitivity to be really important to getting a good match. One rue of thumb I’ve heard from other fans of the SX-X50 series is to stick to speakers with sensitivity over 90db. That’s certainly helped with my pursuit of speakers, and I expect it would be even more important with a 15wpc model.
Now those Sansui don’t have the sensitivity spec listed on the old materials, but just looking visually at them, they look like a model that would require a little more juice. If I were you I would look for smaller more efficient vintage speakers, or modern high sensitivity bookshelves.