I think they modified the page. If you search for GPT-5.3-Codex-Spark, Google still has it indexed with 15x. Searching: GPT-5.3-Codex-Spark + "15x" will show all the downstream sites that picked up the claim.
I don't think the visible page text ever said 15x faster. It's possible they modified it before I saw it, but it's not in the oldest Internet Archive version either.
The other news sites that mention 15x faster are probably either getting it from the same <meta> tag that shows up in search snippets, or from the RSS feed. Both would be generated from the same source text in whatever platform they use to write their posts.