BWV 715 is a set of variations on the "Allein Gott in der Höh' sei Ehr'" chorale, showcasing Bach's skill in elaborating a simple melody. The variations offer a variety of textures and moods.
Achieving a singing tone and executing the rapid figurations with clarity are important technical goals.
Allein Gott in der Höh sei Ehr (BWV 715) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 5.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 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 Allein Gott in der Höh sei Ehr (BWV 715) lasts about 3 minutes.
Allein Gott in der Höh sei Ehr (BWV 715) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.