Like other GeForce cards, double precision performance is significantly less than single precision performance. According to this Wikipedia page, GFLOPS for a RTX 2070 doing double precision math max out at 200-250 GFLOPS depending on model and if it's using boost. If you used singles you should be seeing more like 6500-8000. The card used in that example was a K40c, which can do 1430–1680 GFLOPS double precision.
There are similar other charts on Wikipedia for other GPUs that show their performance results.