I wouldn't use a flush chemical.
Most coolant has pH buffering additives to keep your coolant from getting acidic.
Cooling system flushes are usually acidic.
Doesn't make sense to me, to go through the trouble of keeping acid out of your system and then filling it up with acid.
I also wouldn't use soap, detergent, dishwasher tabs, or any other thing unless I had a known problem with oily stuff in my radiator. Like a transmission cooler leak or head gasket leak pushing oil into the coolant.
I'd just drain, fill, and run with distilled h2o, and repeat until what wind up with in your system is mostly clear. Then add 50%+ of the system's capacity of coolant and top off with distilled.
I'd go now vs. waiting. If you don't know when it was last done the 150k goes out the window if there were previous maintenance intervals that might have been missed. But even if 150k is the first service interval for coolant, there's two big advantages to doing it now: The weather is pleasant and you'll have piece of mind. If it's worrying you, just get it done and stop worrying.