If you want to avoid overdone, do the Clementi instead. Or ask to substitute a Czerny or Weber sonata.
Unfortunately, the RCM examinations system isn't that flexible when it comes to sonata choices for the list B
For Beethoven:
Op. 31 No. 1: This is a relatively light sonata that could be nice on a program. It's about 18 minutes long (without repeats)
Op. 31 No. 2 (Tempest): This is a rather popular choice for exams ... it's a darker and more moody sonata that tends to do fairly well in exams. It's about the same length as the Op 31 No 2
Op. 90: This is a short 2 movement sonata ... the first movement was the soundtrack for the promo of the Minnesota e-piano competition for a long time. A great choice if you have a substantial work chosen from one of the other lists such as another sonata (e.g. Prokofiev sonata no 3), major romantic work (e.g. Chopin ballade no. 4), substantial concert work by Bach (e.g. Italian Concerto/Chromatic Fantasy and Fugue).
Op 2 No 2: A happy sonata with some symphonic moments. The difficulties are subtle than the later sonatas, as this sonata requires a lot more finesse and refinement, as the writing is much more exposed. A rather long sonata for an exam, but still doable.
Op 2 No 3: I played this sonata for my own exam ... examiners know this sonata as the "double-thirds" sonata, as it opens in double thirds (it lasts 4 bars). The plus with this sonata is that examiners will forgive a lot of mistakes later in the sonata if you nail the opening thirds, and have an exceptional second movement (as told to me by several RCM examiners in workshops). THough lots of fun to play, this is one of beethoven's hardest sonatas (everything is exposed and relatively dry). This sonata is 25 minutes long (without repeats).
The moonlight sonata is also a great choice as well, considering you have already learned most of it.