The Shosty is more like 10 minutes I think though. The Poulenc is a pretty awesome piece.
Aside from Rachmaninoff's Suites, check out Arensky's op. 15 - it's gorgeous, especially if you love his no. 1 piano trio! (I don't know the other 4, but I guess they're also great, so maybe check them out too!) Other than that, the Haydn/Brahms Variation (with the repeats it's around 15 mins) or Debussy's "En Blanc Et Noir" should fit the bill.