The ESC/knock system is hearing something. Could be real knock, could be false knock, as the knock sensor is just a microphone & the module a filter.
That means that the ECU is pulling timing to prevent knock. A great rule of thumb is you tune for 0 knock, as any knock is no good. You don't need to hear knock for it to be happening, matter of fact if your hearing it, it's too late. If it is real, things can go poof real quick as you're only at 15 pounds. If you only have 91 octane as an option I'd turn the boost down.
You can look to see if anything is hitting anywhere, causing the false knock? Is it during trans shift points? It could be vibrations, a wiring issue, etc. Knock real or false can be a bit of a wormhole to go down & a bear to figure out.