Johann Baptist Cramer's Op. 15 sonatas are a significant contribution to the Classical repertoire, known for their balance of technical demands and musical expression. They are often used as teaching pieces.
Requires developing finger dexterity for passages that demand both clarity and fluidity.
3 Sonatas (op.15) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
3 Sonatas (op.15) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.