You can make a lot of profit with holding the bitcoin for a pretty long time and I think that if you would do it now you can make big bucks because its going up more and more from now on.
The best time was when it was 100-200$ around but yeah who knows in coming years what price bitcoins reaches so its better to save some bitcoins, which I personally have also done, than to regret later thinking why I did not stock. Basically bitcoin was designed to have huge prices in future with the feature of halving. So, we must make use of it by saving it.
If you go back that far in time, then you could even say that buying at $10-$50 levels was probably the best of the best for semi-early birds.
But realistically speaking, in recent times where you can go back to 2015, it would have been a great shot if you bought your coins between $220-$300 as the price was stuck between these levels for so long.
It gave people enough time to buy themselves plenty of coins. But even then people were questioning and doubting whether or not the price would fall below sub $200 levels again.
Just look at where we are right now. More than doubling your money in just one year is what people's motivation should be when buying at low levels.