There is required, and there is the safe thing to do:
High school Physics:
'08 Car & Driver test of Ranger had it stop from 100 km/h (~60mph) in 51m (~167')
Adding non-braked 1,500lb trailer and assuming Ranger brakes don't fade*, the stop from 100 km/h takes ~68.5m (~225'). That's more/less 60 additional feet to stop.
Adding brakes to trailer - I'll assume they are 80% as effective as Ranger's brakes (trailer tires tend to be harder, etc) would allow stop in ~54m (177')
My wife(fiance at time) and I had one extremely exciting stop on cold wet pavement - truck would have been close to GVWR, and with trailer, we were close to GCWR - where stopping distance turned out to be >140m (>450')! Luckily, I had started stopping ~150m (500'), but the 10+ seconds it took us to stop gave us time to think about what was happening... After which, the little enclosed trailer got surge brakes.
My personal rule of thumb is >40% of empty towing vehicle needs brakes on trailer - about 1,250lbs for Ranger whether it is required legally or not. A shorter vehicle, like my Explorer Sport, needs brakes sooner.
*In the '08 C & D test, Ranger brakes were fading during just empty truck stop from 100 km/h.