Sure, you can stack those sats and sell them in the future when they're worth more, but then you could also just buy small portions of BTC every day.
That is true. How much Bitcoin could I earn by directly purchasing $15 per month of BTC; or how much BTC would collect in a month with mining having the same cost.
About 4TH would give you how much BTC currently, for an average month? So a few sums up, you get around 0.00024465 BTC / 9.62 USD. Less than buying directly.