15 current carrying conductors

[infinity]

In your example would a 10 amp continuous load need to add in the 25% factor or did you mean that the actual load on each circuit is 8 amps?

No, 10A actual load on each circuit. The 25% factor is used for determining the minimum conductor size before any adjustment factors. The final adjusted/corrected ampacity would only need to be 10A for the 10A load.

Don't you find it odd that one section of the code requires the conductor ampacity to be increased by 25% (continuous) and the other part of the code allows you to use the same conductor without the 25% added in?