Tempo rest period

Playing football we use tempo as a form of conditioning along with its usual benefits. The question is … is there a rest period that would be considered to short when doing tempo runs? We do hundreds for tempo in sets of five with 15 to 20 seconds rest between sets (runs are 15-16 sec) and either a 100 yard walk between sets or active recovery between sets (push ups, sit ups, burpees whatever can challenge us that fits the goal of active recovery). Is there a point where to short a rest interval becomes detrimental to recovery? We are conscious of keeping the pace below 75% and therefore see rest between sets as the best way to gain the conditioning we are after. Thus the possibilty of reducing it even further from the above is possible. Charlie would love to hear your thoughts.

when we do tempo 100s we usually do them in one minute cycles. So, if you run the 100 in 15 seconds, you would rest the rest of the minute (45 seconds) then go again…
ARe you finishing the last 100 in the same time as you started? There are a lot of posts here on tempo which you can search for. But i learned that you should be able to start at the pace you started. so if you can finish them in 15 second pace with that short of rest and its not too hard, then your fine. But if your fallin off, maybe you should take alittle more rest. hope this helps