>>531932210
In terms of TOTAL ammo, I think ~15 rounds is justified for a backpackless weapon capable of killing heavies. If we vaguely abstract the killing power of the epoch to needing 2 rounds to kill a heavy where a RR needs 1, then the epoch slightly pulls ahead in that the RR can kill 6 heavies with its ammo supply while the epoch can kill 7 and a half. Someone can potentially even argue that the epoch currently has slightly too much ammo, but I think the current overall max capacity is acceptable considering the myriad of drawbacks that the weapon has and the fact that any preemptive reloads drastically cuts into total ammo supply.
If I were to change things, I would decrease the number of spare magazines that the epoch has but increase the capacity of the magazines. This would give the weapon greater ability to more efficiently sustain itself from POI ammo boxes. For example, 5 round magazine with 2 spare mags instead of the current 3 round magazine with 4 spare mages. Both are 15 rounds from a fully loaded state, but the larger mag option sustains itself better and is less likely to need to reload halfway through a kill.