I started cycling 10 years after I had to give up running due to knee problems. I had to do something to retain the fitness that I still had and Tried a bike ride with a few other mates and still riding.

Think it depends on you but Back and knee problems from running hit many of us that used to do it. Sounds as though you enjoy Running and cycling and to "Retain" your current fitness you are probably doing about the right distances but if you want to improve in either discipline then more mileage with more effort would be required.

Says me that is struggling to find time to get out on the bike and am barely doing 100 miles a week in all that spare time I have since I retired.