Hello gunjun,
we had a very similar situation last year when we inquired about the individual interest rates, and I also find 2.4% almost outrageously high without knowing the exact key data. When searching on the internet, you should especially always do one thing and search for cheap construction financing in the private browsing mode of the browser. Unfortunately, it is also like searching for a trip in that the individual sites create cookies and can remember how often you have already visited the site. This usually causes the interest rates to be artificially increased.
In the end, I came across a very good site that supported me very well with my construction project and also sent me completely non-binding offers from several providers. There you will also find a construction financing calculator, which offered me very good interest rates. Further info gladly via PN.
I hope I could help you a little and wish you continued good luck with your construction project :
Regards Frank