I generally prefer a faster approach for this piece, but I think your slower version is equally valid. My favourite recording of this music is by Sofronitzky - swift and light fingered in general.
In my opinion, in many lyrical pieces, its actually easier to have a convincing interpretation with a moderately fast tempo, since this allows the music to flow naturally. Also, with a faster tempo, I feel there is more scope for rubato and "stretching" the tempo at places. Whereas at a slow tempo, it often takes much more concentration to make the interpretation work. There's less leeway to stretch the phrases at a slow tempo, as one will run the risk of it turning static. This means that a steadier tempo is often required - which could run the risk of a boring interpretation. A slower tempo also tends to expose more details. phrasing and tone, which often means one has to be far more precise than in a faster interpretation. But when a slow interpretation is well executed, the concentration and emotional intensity can be staggering. Think of Richter in some of the slower Rachmaninoff etudes (Op 39 no.2) for example, or playing Tchaikovksy's June from the Seasons - slow and steady, but with such a gorgeous tone, and the rubato (if any) is very subtle.
I think your slower version is convincing in its own way, and whether one prefers the other is just that - a subjective preference, and nothing more.
Topic: Much, much faster playing of Impromptu op.51 (VIDEO)