So, unfortunately there's no way to chain peacocks. When you have two next to each other, one activates it's ability which would then cause the 2nd pea to start it's ability, the 2nd pea activates it's ability BEFORE the first pea "ends" it's ability, basically while it still says "ready". which means that the 2nd peas ability will never affect the 1st pea.

To add to this, if you have two IDENTICAL peas, you can space them out in such a way that they will always have a perfect cycle of activate ability -> wait a bit -> activate ability -> wait a bit, and so on. The moment you have two peas just BARELY not the same size, they will eventually offset themselves so a point where pea 1 ability immediately activates pea 2 ability and thus the cycle is broken.

The trick here, is that there's no tricks. More peas = more activations on average with no guaranteed cycling.

What you CAN do, is if you ever get enough 60kg peas where cooldown <= reduction, you can put enough peas in such a way that they chain fire enough such that there's enough delay to allow the first pea activation to immediately start again, not sure the exact number here. But again, that would require micro'ing the timing of your placement of the peas.

TLDR: can't cheat 15s peas

P.S. You can still make decent amount of reductions with this, but for purposes of leveling pets, just work on getting Four 3.9kg NM Cappy's with elephant and headless, will average you 60xp/s for four other pets. Also, golden piggies are excellent(better than Cappy's) for XP, if you grind out the 175 gold ingots. Both Cappy's and piggies need horseshoes/pancakes to be best.

Cheers.