This is Charles-Valentin Alkan's transcription of Mozart's Piano Concerto No. 20 in D minor, K. 466. It is a highly challenging work known for Alkan's dense arrangements and virtuosic demands, transforming the orchestral score for solo piano.
Requires extraordinary finger strength, rapid arpeggios, and massive chordal playing.
Beethoven's Piano Concerto in D minor, K 466, Transciption is rated Henle level 9 of 9 — virtuoso repertoire, roughly concert / virtuoso level. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 9 — meaning you can already play level 8–9 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 Beethoven's Piano Concerto in D minor, K 466, Transciption lasts about 10 minutes.
Beethoven's Piano Concerto in D minor, K 466, Transciption is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.