Your sample size = 5 with no roommate plus 5 with a roommate plus 5 roommates = 15. I think the representative sample size needs to be bigger, at least 5% of the 10,000 or at least there should be multiple simple random samples (srs). In your case, the inclusion probability = 15/10,000 (0.0015), using one sample (or the sum of probabilities for multiple samples). Then, the H-T estimator is calculated by the sample (or sum of the samples) divided by the inclusion probability :)