would you take the cheapest G rated 16 inch tire over the most expensive E rated 15 inch tire regardless?
Absolutely not...... as a commercial grade 16" G ST tire @ 110 psi has 4080 lb capacity and is way too much tire on a trailer that has 15" tires.
A 16" LT G has 3750 lb capacity
There is no benefit of a G tire in this application unless your running 7k axles or max loaded 6k axles.
For a trailer with 15" E tires @ 2830 lbs capacity a upgrade to all steel ply carcass commercial grade 16" LT E at 3042 lb capacity will net you up to 50k-60k miles and 7-10 years of service.