Johann Baptist Cramer's Op. 15 sonatas are exemplary of his pedagogical and compositional skill in the Classical era, often featuring beautiful melodies and well-crafted structures. The set includes pieces that are both technically engaging and musically rewarding.
Focus on developing a smooth legato line and controlled dexterity in faster passages.
3 Piano Sonatas (Op.15) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 7.
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 Piano Sonatas (Op.15) lasts about 12 minutes.
3 Piano Sonatas (Op.15) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.