I've played this prelude so know it well.
First, let me say that I think the most prevalent error in playing No. 15 is taking too fast a tempo in Part A and its later reprise. The faster it goes, the less the sostenuto effect to the ear. Also a more restrained tempo there brings out through the ostinato figuration the sense of a gentle rain falling on a gloomy day.
As for Part B, Chopin himself gives no indication by using a tempo marking per se, nor does he place a direction there such as piu mosso or agitato. We all need to take note of that fact. In the Paderewski Edition, there is nothing written in the editorial board's commentary concerning measure 28 at the start of Part B, and their comments through measure 75 concern themselves with notational details only. Part B, of course, is more like a heavy squall in comparison to the opening gentle rain. It starts sotto voce but soon builds in tension and bombast with the crashing chords and octaves at the height of the storm. This in itself is an aural departure from the subdued and lyrical Part A, thereby creating its own drama.
Having said that, some pianists do pick up the pace there. My own opinion is that if you choose to do so, it probably should not be a radical departure from Part A, but could certainly be enough of an increase in tempo so as to be noticeable and assist in the change of mood there, but not so much as to sever the connection to Part A and its reprise. Those thunderheads developed out of the very same clouds earlier producing the gentle rain. Had Chopin wanted an audacious change there, he certainly would have called for it. Thus, you'll need to meld your interpretation to take your desired liberty there, but also to serve the composer above all else.
That's my 2 cents.