This is a clever canonic composition by Mozart, showcasing his mastery of counterpoint and his ability to create complex textures from simple material.
Maintaining precise rhythmic independence between the voices is the primary challenge.
4 Puzzle Canons. K.73r is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 3.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 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 4 Puzzle Canons. K.73r lasts about 2 minutes.
4 Puzzle Canons. K.73r is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.