I dare say the amount of users who have native IPv6 connectivity is higher than first thought. Most of the large ISPs are IPv6 first with IPv4 as a service. Thus the translation for IPv4 is slower than native v6.
I’d be very surprised if your host charges for IPv6, if they do, I’d consider moving elsewhere.
You could try cloudflare (free plan is available) however looks like your with krystal for hosting. Cloudflare would allow a passive proxy and would be able to serve IPv6 now as default also offers HTTP2.