Seeing it on your PC
steam.exe or a game connecting out to these ports while you play.
Should you block it?
Normal for Steam. Only a game server you host needs them incoming.
Check it on your PC
Run this in PowerShell to see what is using port 27015 right now, and which program owns it:
Get-NetTCPConnection -LocalPort 27015 -ErrorAction SilentlyContinue | Select-Object LocalAddress,LocalPort,RemoteAddress,RemotePort,State,@{n='Process';e={(Get-Process -Id $_.OwningProcess -ErrorAction SilentlyContinue).ProcessName}}Get-NetUDPEndpoint -LocalPort 27015 -ErrorAction SilentlyContinue | Select-Object LocalAddress,LocalPort,@{n='Process';e={(Get-Process -Id $_.OwningProcess -ErrorAction SilentlyContinue).ProcessName}}No output means nothing is using the port at the moment. For every connection at once, paste netstat -ano into the netstat explainer.