Koga roadrunner

I have a beautiful Koga roadrunner on which I have cycled a lot of km’s on and did quite some tours. I feel like the bike is super heavy and even with little weight on it, it cycles heavy.
If I’m on my roadbike, I’m going 1,5x as fast with the same amount of effort.
I’m looking into maybe getting a new bike for biketours (gravel?) but the weight of the new bike would be almost the same, so how do I make sure the bike i buy cycles lighter, or can I do some adjustments on my current bike to make it more sporty/easier/faster? Was thinking different handlebars?

Since these pictures the wheels are now marathons, and the chain and gear is renewed, but at the moment I don’t have better pictures.