I've calculated on some fast trainers, and I get something like 24-26 ability increases for 100 condition loss.
Now I don't have access to the best drills yet and you may find some better fast trainers than mine.
So I would make the calculations with 30 increases for 100 condition loss
(as I said previously, I found that friendly game average a bit over the above 0.3 but the problem with them is they're more time consuming and the abilities that increase are more random as opposed to a training program where you know what abilities are increased. however for raising SA and extra positions, it's worth looking into)
So with the above, 4.5% per 15% condition loss, 28% = 97 rest packs
We can conclude also that every % under 99% we buy our player requires 3.5 rest packs to gain