Thanks a lot for this hillclimb track . When I was young I assisted to the victory of Gerhard Mitter and Rolf Stommelen. I recognized in your work the green where I was sit to see the passage of the cars.
This is really well made that I don't really believe it's your first map. Agree with others the lag on this is a thing. I've look at your map for a bit, these might be the reason: a- check your actual mesh count on your exported version, you don't have much, but it might be too separated I'm not sure. b- which is your most possibly reason, is your texture. Your textures' resolution are too high, probably need to low down for a bit.
Apart of that it's a fun course, I'd love to see a better version and drive again.