There are many pieces (not limited to Bach) that merely arpeggiate chords. In such cases, extracting and playing only the chords helps to understand the harmonic progression and makes it easier to grasp the structure. For example, from measure 15, try playing the chords written in the treble clef consecutively with only the right hand, without arpeggiating them.

For instance, one might consider: measure 15 p, measure 16 mp, measure 17 p (as it returns from dominant to tonic), measure 18 mf (as it's a borrowed chord), and measure 19 mp (as it's the resolution of that chord). However, considering the approach to the soprano G, which is the peak point in measure 20, a dynamic flow of mf without decreasing volume, leading to f in measure 20, can be created. This is just one example, but by simplifying the chords in this way and playing them in a shorter time, you can understand the character of the chords and the mood of the passage, and thus know how to approach each chord.

At the beginning, the second phrase starts from the upbeat of the third beat of measure 4. Please do not overlook that the inner voice forms an independent melodic line (starting from the top of the bass clef: B, B, C#, D, then moving to the treble clef: E, E, E, D).