Learning at your own pace is very important for not under- or overwhelming yourself in the long run with returning reviews and leeches. At times, i was also very insecure when i heard that some people have an average level up time of 7 days or something in that range, while i was going much slower. So i started to accelerate and burned out over the course of a few levels, which led to piling up reviews and me losing motivation because accuracy was getting lower and lower. It then takes a lot of effort to tackle a 500 - 1500 review pile over the course of a few days. So most importantly: Don’t look at other people’s level up speed, because your learning style may differ from others’.
Here’s a tip however that worked for me to get my average level up time down:
When reaching a new level and doing new lessons, make sure to time them so that you do the first review of new items on the same day. For me, when i do new lessons late at night, then sleep and do the reviews in the afternoon of the next day, i forgot a lot more, as opposed to when i do lessons in the morning and the first review in the evening. The fast review seems to make items stick more, at least for me.
Here’s a screenshot of my level up times in the 30s and 40s which varied wildly! And you can see the burnouts there as well…