The real trick to getting work done is that my 15 minutes is very seldom only 15 minutes. It’s just the threshold.
If 15 minutes doesn’t work for you, imagine a lower threshold. Imagine 5 minutes. Imagine a broom handle lying across the floor. Fall over it.
Conversely, you may need an even number. So try 20 minutes. Many years ago when I was trying to get up early in the morning (before my infant twins were awake) to work on my doctoral dissertation, a friend suggested that I try getting up on the half-hour, when the clock’s hand was rising rather than falling. I don’t know why 4:30 was “better” than 5:00, but it worked.
Lowering the threshold will work for your other unresolutions, too. When I’m having trouble getting myself to the gym, I coax myself into merely putting on my workout clothes. Just put them on, you don’t have to go. Then once I’m at the gym (I’m dressed for it, so why not?), I tell myself, just get on the treadmill, just walk for a half mile, then you can quit. Once I get started, I almost never do less than my 2 1/4 miles.
Lower the threshold. Stumble over it.