So I've made it clear to my players far too many times to count that I dislike Fit/Very Fit as written. I allow them, because they are valuable and not-unfairly priced, and because they are extremely popular.
But I don't actually like them.
Mostly it's because it folds a pair of very valuable effects (FP recovery increase, and HT roll bonuses) into a single trait in such a way that it's an almost automatic purchase. It has a way of distorting HT, too, in that it's not worth 10 points for +1 HT unless you a) need +1 to HT to get a whole number in Speed, or b) you already have Fit.
Very Fit is rarely taken, because its benefits are good but HT is perceived as a better choice for the same cost.
But what if we split it up differently? Here is one option.
Fit doubles your recovery of FP while resting. Instead of 1 FP per 10 minutes, you recover 1 FP for 5 minutes. This does not affect FP expended to power supernatural abilities, spells, etc. or FP lost to starvation.
Fit also gives a +2 to HT rolls against FP loss from exertion from running, swimming, and similar activities (p. B354-355). In addition, it gives you a +2 HT to determine how long you can hold your breath (p. B351).
As Fit, but in addition you expend half as much FP for physical exertion, such as running, swimming, digging, combat, etc. Very Fit gives a +4 to the HT rolls listed under Fit.
Basically, this nerfs Fit/Very Fit as a cheap way to stay conscious, resist poison, and not to die. It greatly increases its value in games with physical exertion, however, by making its focused HT benefits much stronger. A HT 12 Very Fit character has a 16 HT for holding breath, will be able to run for long distances without getting tired easily, will be able to march around with heavier gear and still be just as fresh as a more lightly equipped friend at the end of the hike, etc.
It also means Fit/Very Fit maps very well to improved aerobic recovery, not endurance per se, so you bounce back faster from bouts of activity.
I'd still do Mana Recovery 1 and 2 as 5/15, and simply have them give 1 per 5 mins and 1 per 2 mins recovery of any/all FP/ER expended to power magic. If you really want to be super-fit physically and recovery magic energy maximally we're looking at 30 points, but I think the two traits above might work well for that.
Not that I'm using either for my DF game, it's too late now, but I like the idea. It makes Fit more about fitness and aerobic recovery, not about being harder to kill, better at staying conscious, and more likely to fend off disease and poison. All of that is what other traits are for!
Important note: It's worth pointing out that if you want to re-tool FP more deeply, you will want to take a look at Douglas Cole's excellent article The Last Gasp in Pyramid magazine. My post isn't about re-tooling FP, or changing how/when/where/why it is expended or recovered. It's entirely about re-tooling Fit and Very Fit so they are less "HT bonus with side benefits" and more "recovery traits." If you like things how they are, or if you want to change things are a far deeper level and in a broader way, the revised advantages above aren't aimed your direction!