I cannot give even a reasonable estimate of probabiity IRL without knowing a bunch of things, spending way more time on this than would behoove me, and let's be real, actual experts in this field are still learning about this virus.
What I can give you, however, is a more refined understanding on probability.
Let us just take your numbers at face value and say that 0.3% of the population has the virus and the false negative rate is 15% so that odds that a given individual has the virus and and tested negative is 0.045% or a probability of 0.00045.
Then if there are 100 people there, the odds of at least one person having the virus and testing negative are 1-0.99955^100 which = 4.4%. if 200 people, 8.6%. If 500 people, 20%.
If we assume 3% of the population has the virus and a 15% false negative, then we if there are 100 people, then P(at least one positive person with a negative test result) = 1 - 0.9955^100 = 36%. if 200 people, 59%.