Interesting question! (Where does that 152 figure come from?)
How many torps per fight? When Kirk orders "full spreads" fired, we might be talking about six torps at every command of "FIRE!", considering that in "Journey to Babel", he used classic submarine movie jargon and ordered "torpedoes 2, 4 and 6" to be fired, suggesting six forward tubes. And in "Elaan of Troyius", six indeed was the number of torps visually confirmed when Kirk fired a "full spread", and that put an end to the fight against a fully shielded Klingon battle cruiser.
However, there were misses among that full spread. And when that spread of three misses the wildly maneuvering foe in "JtB", Kirk doesn't seem to bother with further ones. Perhaps torps in TOS are supposed to be used WWII style: they are short range weapons, powerful enough to ensure a kill if there's a hit, but unlikely to score hits at longer ranges or higher speeds. In those realms, guns, that is, phasers, are the preferred weapon.
Quite possibly, then, just three to six torps expended per average fight, mostly as mercy shots towards the end of the battle. That is, if Kirk considered sinking the enemy a merciful thing. But we know he has other, more enlightened ideas of mercy (he wages war with his hand phaser on stun in "Errand of Mercy"!), so torps might actually see very little use in "conventional" fights.
But how often does Kirk fight conventionally? He was willing to try a single torp even against the tiny NOMAD in "The Changeling", so supposedly any foe that is foolish enough to come within torpedo range will get some. But many of Kirk's fights are actually long range, high speed chases. The dikironium cloud gets phasers rather than torps, say. And quick-reaction fights rule out torps, too: there are no torps used in "Balance of Terror" or "Errand of Mercy".
I'd say a loadup of 152 could allow for monthly battles at the rate Kirk is going. Then again, Kirk gets opportunities to reload at least once per season, visiting starbases or major colonies or locations where he can pick up Galactic Commissioners and other nasty things like that. It's not really a "five years out there, then back to civilization" type of deal at all, but rather a "business as usual, oh, has it already been five years?" one - only retroactively defined as having ended at the five-year mark.
Doesn't mean Starfleet wouldn't stock up for five years sharp anyway. I mean, "Mark of Gideon" explicates that the supply of food onboard is going to last the whole crew for five years. Then again, that's at least a couple of years into the mission already - so the policy might be to always keep the ship stocked up with five years' worth of everything, even during the last year of this five-year mission...
Timo Saloniemi