{Unsolicited opinion}

I think you should replace that T connector with a 3-way Jandy valve so you can isolate/throttle the booster pump and pressure side cleaner line from the main return flow. If a 3-way is too expensive, then you could also just have a simple Jandy shut-off valve (I don't like ball valves because they tend to leak, but that would be an even cheaper option). This way, when the Polaris is not running, you can completely isolate that line. HOWEVER, if your Polaris booster pump is automated or timed to regularly go on and off, then isolating that line could cause the booster pump to dead-head (pulling on a dead line) which would burn out the booster pump.

I say this because I don't like the idea of having that 1-1/2" (?) pressure cleaning line always open to return flow especially with all that flex tubing. If that flex tubing and/or couplers should spring a leak, then you will have your pool water return line open and you'll flood your equipment pad.

Also, I'd very carefully inspect all of that flexible tubing and couplers for leaks. After 15 years, it's entirely possible that you could have a leak there....

{End of Unsolicited opinion}