Converting .m2ts files to .ogv format.
Converting Blu-ray BDAV Video Files directly to Ogg Video File (.m2ts to .ogv conversion) is certainly possible, and should be quite straightforward, even though your options are limited.
Your best bet appears to be using the Freemake Video Converter.
Alternatively, you can try some of the online conversion solutions that also appear to be capable of converting .m2ts to .ogv.