Bob appeals to the musical notation of the Masoretic accents. This is a technical subject outside my expertise. I agree that v. 15 is not a question, for reasons I have already explained. That said, Bob's argument – assuming it is correct – may tell us something about the early medieval interpretation of the psalm. But it does not necessarily illuminate the psalm's original intent.
The root חסד (ḥsd) is often translated as "kindness" or "lovingkindness" or the like, but its root meaning is "covenant loyalty." The two concepts have some overlap. The translation "lovingkindness" usually works, although not always. For example, in Psalm 136:10, God smote the firstborn of Egypt out of ’covenant loyalty’ to Israel. But "lovingkindness" doesn't fit. Similarly in verses 15, 17-20.
The meaning of (חסידיו) ḥsydyw in this verse would be an interesting topic for discussion.
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