Calculating charge time of a large capacitor from a boost with a limited power source
If you're pulling constant energy from the input, and putting all of it (or a constant proportion of it) into the cap, then of necessity the capacitor current will change over time as it charges.

You can calculate this, and find that the initial capacitor current is -- inconveniently -- infinite.  But you can certainly take your 135mJ and divide it by 2.5J/s to get a lower limit on the capacitor charge time.

To really minimize that charge time you'd have to give some love to your boost converter.  This is basically what photoflash and capacitive-discharge ignition systems do, but even that has limits -- basically you end up being current-limited in your coil and switching element, and while the upper limit isn't infinity, because of finite switching speeds, it can still be arbitrarily large.