Mozart's '6 Notturni' are pieces for two orchestras or ensembles, not solo piano, and would showcase his mastery of orchestral textures and contrapuntal writing. This entry is likely a misinterpretation for solo piano.
This is an orchestral work, not for solo piano, and therefore does not have piano-specific technical challenges.
6 Notturni is rated Henle level 6 of 9 — advanced repertoire, roughly ABRSM grades 7–8. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 6 — meaning you can already play level 5–6 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 6 Notturni lasts about 4 minutes.
6 Notturni is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.