The rich deposits of gold and high-quality silver ore turned Virginny Town to Virginia City, the most important settlement between Denver and San Francisco. They also prompted President Abe Lincoln to make Nevada a state in 1864. Although it did not contain enough people to constitutionally authorize statehood he needed the Comstock to secure enough electoral votes to win the 1864 election.
I don't think there is a restriction in the constitution about the number of residents required to make a state, though there may have been some guidelines developed in one of the Congresses along the way (e.g., guidelines for the number of people to be represented by each representative in Congress).
I think a more correct characterization of Nevada at the time would have been that it only had about 15,000 residents and that was really too small to shoulder the burdens of state government, taxation, etc.
15,000 is about the present population of the city of Great Bend, Kansas. Hey, want to be a senator?
Others, such as Charles Dana who was in the War Department under Lincoln, said that Lincoln pushed for Nevada statehood to get the 13th Amendment through the Senate because a nose count at the time showed that the votes of senators from one more "state" was needed.
The population of Nevada in 1870 was about 43,000. Over 12,000 people voted in the statehood referendum in 1864. Your 15,000 population is wishful thinking, as is your conspiracy about Nevada statehood to begin with. Lincoln got 212 electoral votes in 1864 to McClellans 21. He didn't need Nevada's three.