If you're a relative newcomer or you have blown your stash thinking you have years to faff around and accumulate my advice is do whatever you can to accumulate 1 Bitcoin before it reaches 100k. Once that's reached and its on it's way to 200k it's going to become very difficult to accumulate for regular folks. If you can jumpstart your entry by borrowing 10k, 20k or 30k from the banksters do it - Have no fear! Buy $20 chunks as often as you can, pay no heed to the price. Ditch your daily $5 Coffee - that's $150 of Bitcoin per month, stop the pizza delivery, buy $15 of BTC instead. A few small changes in lifestyle and you will be surprised how much you're accumulating. During the journey you may want to punt a portion of your BTC on an Alt you believe will rise greatly - be careful though and do not panic if your alt crashes because 99% of the time they will recover to the price you bought in at.
The prime directive is to increase the amount of BTC you own, nothing else matters
While I agree with the premise of your post at the same time it is not as simple anymore, buying 15 dollars worth of bitcoin at a time will generate massive fees in the future so it is better for you to make all the savings that you can do in a month and buy bitcoin once a month, this would require some patience and you are not going to get the best possible price with this strategy but it is going to be cheaper over the long term.