You might not be on a repeater channel. 1-22 are simplex channels, which transmit on the same frequency they receive. But there are eight repeater channels which allow the repeater to transmit while simultaneously receiving. Doing both at the same time is called Duplex. Different manufacturers denote those channels differently. Some continue the numbering scheme and refer to them as channels 23-30, others repeat the 15-22 numbers but prepend or append RP to the channel, like 15RP, to indicate that they are repeater channels.
Repeaters receive on the 467 MHz main frequencies and transmit at exactly the same time on the 462 MHz main channels. That’s referred to as an offset and it is generally exactly 5.000 MHz for UHF channels (in ham radio also). They need an offset to be able to transmit while receiving. So, in your radio there should be eight repeater channels which are programmed to receive on exactly the same 462.xxx frequencies as 15-22, but which transmit on the main 467.xxx frequencies, where xxx is typically the same for both. You need to use one of those.