I'd rather have it on a regular basis than $15 to $100 in a few weeks which is sometimes hard for us so $15-$20 isn't too much pressure but you still have to balance it with other needs even if you have extra funds.
I agree with the last point you made because acting according to our level of ability is a pretty good thing, because the investments we make do not become a burden in our lives. I've seen several posts that the investment they made in Bitcoin became a burden on their minds. This was caused by their aggressive decision to buy instantly. So they appear unprepared when prices fall because they do not have asset reserves to accumulate at low prices.
So, for that reason, I don't like to act more aggressively, but I regularly buy even in small amounts. In other words, I invest for the long term so I can continue to buy at every stage. But I also don't oppose those who act aggressively because they have found great planning in their investments so they have thought about the decision beforehand.