Enable Proxy made my resful APIs super slow on 3G/4G

Hi there, I am enabling DNS Proxy on my CloudFlare account for my website/APIs. However, I got a very serious issue with 3G/4G in VietNam. I tested API from my application in 4G (viettel provider). It's super slow. I took about 30s to just get a simple GET api from my server. When I tried the API directly from web (Chrome), it's working fine. Is there anything I can do to solve my issue?