Joachim Raff's Op. 99 Sonatinas are polished Romantic miniatures, often characterized by their elegant melodies and sophisticated harmonies. They are effective in developing expressive musicality.
Focus on creating a singing tone and shaping phrases with subtle rubato.
3 Sonatinas (Op.99) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of 3 Sonatinas (Op.99) lasts about 15 minutes.
3 Sonatinas (Op.99) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.