If my quick maths has the correct assumptions, then we can store 225 Petabytes of data in the balls.

Human sperm contains about 3 million base pairs (haploid genome).
Each base pair of DNA (A, C, G, T) is encodable with 2 bits.
3 million * 2 bits / 8 (to convert in bytes) = 750 MB.
Using a rough and imprecise average of 300 million sperm cells stored in testicles, we get:
300 million * 750 MB = 225 PB.

Plenty of space for your savegame data!