How would you differentiate between 15 million and 10,000,005? Wouldn't they both be elfu kumi na tano?
15 million would be milioni kumi na tano and 10,000,005 would be milioni kumi na tano or kumi milioni na tano, none of them would be elfu kumi na tano.
In speaking, in order to differentiate, I've noticed that Tanzanians just make it obvious by tone of voice and/or pausing:
Milioni kumi...na... tano (10,000,005)
Milioni... kumi na tano (15,000,000)