In bacteria, dormant viruses in the genome are called prophages. I found one paper, in eight E. coli strains, between 8-22 prophages were predicted to be found in each strain's genome. E coli genome is approximately 5.6 Mb. Prophage genomes were from 5.6 to 131.9 kb, say on average 70 Kb. So on average, (14 prophages x 70,000) / 5,600,00 * 100 = 17.5%. Very back of the envolope maths, and only for E coli, results will vary wildly. https://www.frontiersin.org/articles/10.3389/fmicb.2019.03093/full