Speed is relative. On my heavy 'all-purpose' bike (Ti CX with 28mm road tires) I might average 15.5 mph on a solo 50 mile, 4000kft climbing day. On my race bike; same ride maybe 17-18 mph solo if motivated. In a fast group, whatever the group averages; 21+ mph, assuming I'm on form.
However, I haven't ridden with anyone in about a year (stupid pandemic), so my fitness is down and my weight is up. I've got my homework to do if ever getting back to these speeds.