Pallas I'm feeling discouraged at how long it's taking me to do my lesson pieces
As a child, I did the first two grades in one year. For the longest time, I thought I was slow at arithmetics. I wasn't, I just had one year less of practising arithmetics compared to my classmates.
You make fast progress. That means that you haven't learned as many pieces as most students have when they get a new piece. That explains why you think it takes you such a long time to do your lesson pieces.
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... feeling like the pianist on the Titanic ...