$ time curl --silent api.telegram.org --output /dev/null real0m5.577s
Doing a IPv4-only request was quick:
$ time curl -4 --silent api.telegram.org --output /dev/null real0m0.090s
Inspecting the network traffic with wireshark shows that two DNS are made: One for the IPv4 address, one for the IPv6 address.
The IPv4 address is immediately resolved, but the IPv6 request is cancelled after 5 seconds: