Aleksandr Glazunov's Op. 54 Impromptus are substantial pieces characteristic of the late Romantic Russian school. They often display virtuosic passagework alongside broad, lyrical melodies.
Requires significant stamina and control for the rapid runs and octave passages.
2 Impromptus (Op.54) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7.
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.
2 Impromptus (Op.54) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.