There will be tons of upgrades to improve performance responses. So what I say doesn't mean much.

IMO, increasing your distance or speed will be more a product of your cycling ability. In your case you are averaging 15-17mph which is not bad at all, so you probably just have to log more miles and get stronger before you buy a replacement bike.

A lighter frame and components that are static and are not moving will not make any more impact than if you lost 5 lbs because it is still the total mount of weight you have to move (not factoring quality). It may feel more nimble, handle better, sprint better, etc. but being able to ride 60kms/125kms and how fast may not be any different.

That said, from my unscientific experience, the best upgrade that someone can make is going from bad heavy wheels to good lighter wheels. But they don't have to be race wheels. I have swapped out 2500 gram wheels with lower quality hubs for 1800 gram wheels (that are not really light) with good hubs and I can tell the difference.

Will you be able ride farther and faster? Maybe not significantly, but if I am trying to ride faster I find it easier and more enjoyable with lighter wheels.

John