Though I think it depends on the amount of bitcoin you wish to accumulate and also the amount you're investing with, but i still wonder what will be holding an investor from not reaching the status of overaccumulation before this 15 years. However, i think the idea of buying bitcoin aggressively when you have already reached the status of overaccumulation does not make much sense to me, if i get to the status of overaccumulation i will take it very slowly, i can decide to buy every dip since i have build a very large portfolio. is only those no coiners/ low coiners that is advised to invest in bitcoin without paying any attention to the market fluctuation by using the DcA method, as a no coiner/low coiner and you're hoping to buy every dip definitely it will take some couple of years before you can be able to reach your target. But when you're using the DcA method you won't even consider the market value before investing, and this is going to make the accumulating process keep moving instead of waiting for the market to dip before investing.
How many Bitcoins are enough for a person is a subjective thing. For a person like me who hails from South Asia, 5 Bitcoins will be sufficient but a person living in USA or EU has different criteria of enough Bitcoin. But that's correct that once you are having enough Bitcoins then don't go for aggressive accumulation of Bitcoin because all of us are gathering Bitcoins to achieve a specific target and if you already have achieved that target then just relax. It might be a good point for you to start selling some portion of your Bitcoins to enjoy the result of their hard work .
For no coiners, the best strategy is to start investing from any point and once they start investing they can go aggressive on dips only when they figured out what actually a dip is.