If I were you I’d drop to -1.0 rather than -0.75. I don’t know how much lenses cost, but I’d do quarter-diopter steps instead…
OK, I see your second comment. Yes, if you’re really seeing 20/15 a half diopter drop doesn’t sound crazy. There might still be some merit to running around for another couple of weeks with 20/15 vision though. The thing you don’t want to do is get too comfortable with blur where you start seeing it and don’t do anything about it because you’ve got good at living with it.
It’s probably a dumb analogy but you could get used to being slightly drunk all the time and perform well enough that maybe nobody would notice you were drunk, but it would still be inhibiting your performance. Another couple of weeks with your -1.25 contacts would help make sure that 20/15 is the “baseline” you are expecting to see, and not 20/25 with flashes of 20/15.
As for sports with no correction at all, you might be able to do it already(?) It sounds like you’re in the “last diopter” territory now. Generally the approach when you get down to tiny levels of correction is to just wear them when you’re tired or you think it might help. Probably after a few months at -0.75 contacts if everything is going well for you, you could just ditch the contacts altogether, maybe only wear them at night or when you feel like it.
If I were you though I’d still reduce 0.25 at a time. You might still be making improvement now with the -1.25 lenses down to 20/10 or so since with full correction you see 20/10 (or better). I’m not convinced you’ll improve faster with -0.75 contacts than with -1 contacts. It’s totally your call though. If that 20/15 line is perfectly clear go ahead and reduce.
You might also play around a little and wear -0.75 most of the time and wear -1 during an actual game or when you need peak visual performance. I was just reading something that claimed in Major League Baseball the average (uncorrected?) visual acuity is 20/12.