I mean how high can Bitcoin realistically go in the next 2-3 years? £150k maybe which would be less then 10x compared to other altcoins that can 20-50x when the bull run returns.
No one knows for sure, everyone will probably shoot one from the corner of his room. The future of bitcoin is still very good, actually you should cultivate optimism about it if you really invest in it. 20x - 50x from now will definitely be difficult even in the next 2-3 years, but since bitcoin price is uncontrollable it is possible to achieve it in the future.
Advice for you: Be a wise bitcoin holder. You may need to take profit at price x by selling it while you can buy again in the next phase of the decline. Accumulation and DCA are great, but of course I think that strategy is for those who have a steady monthly income.