AFAIK, there is no direct way to do such a check.
I assume that it could be achievable -as a workaround- by getting what's the latest released iOS version from an external resource, it could be something like Apple RSS feed -or a similar resource- and compare it with the current device iOS version, using systemVersion:
The current version of the operating system.
as mentioned in this answer.
For instance, you could request an api that might be built by your team to get what's the latest iOS version and resend it to your application to do the comparing.
Hopefully, if I found an appropriate external resource for getting the latest iOS version, I will add it to the answer :)