Not sure exact comparison that you are trying to make but here is the thing. 1 Bitcoin in 2015 is equivalent to 1 Bitcoin in 2025 and so it's going to be the same in coming years, the changing factor is the fluctuating price, it was never like this in 2015, even on 2030 it might not be the same but we hope for better price ahead.

Short term can be varying between the time the Bitcoin was bought and the Bitcoin was sold, most often the simple logic is buy lower and sell higher. The last time we had the worst dip was November 2023 when Bitcoin tank as low as $15k but now it's trading at $$115k, that's over $100k unrealize profit. This happen within the space of 2 years and some month but do the comparison with another person that bought at December 2018 at $15k and still holding till now, that's 7 years and some months differences with same profit. Similarly, If you have bought Bitcoin when it was trading at $300 in 2015, the same Bitcoin is going to be worth $115k today, that's roughly over $115k profit.

The difference only here is each individual purchase price but 1 Bitcoin is 1 Bitcoin.
However, if you are looking at yearly growth of Bitcoin in each year, the highs and low price, this site has historical data and growth of Bitcoin for each year
https://charts.bitbo.io/price/