OGG describes a container family
The .ogg extension often contains Vorbis audio, but Ogg can also carry other codecs, including Opus. MP3 is a different audio format. The extension alone does not tell you the exact encoding settings or whether the source is a music track, voice recording, or a stream capture.
If sound quality matters, identify the source codec and its bitrate or sample details when available. Converting a low-bitrate source to a higher-bitrate MP3 does not restore information that was already discarded. The new file may be larger without sounding better, so treat the conversion as a compatibility copy rather than an upgrade.