You should count on your builds having only 15 minutes to complete their build command. The additional time for processing and uploading will be added to that and do not need to complete within that initial 15 minutes, and in some cases for very large sites or if our system is busy, they may stretch out to minutes or even an hour (the latter only for tens of thousands of new files in a deploy).
Around unexpected timeouts, I’d suggest some reading here: [Support Guide] Hung or stuck, but seemingly successful build . There are builds that legitimately run for more than 15 minutes, but most cases are something like that: “oops, I started a server” or “my framework left some processes running that made Netlify think the build wasn’t done yet”.
Regarding build resources, what you are guaranteed on our free and Pro plans is identical: approximately 1 CPU and around 2Gb of memory. You may get more - these containers run on machines that could hold 5 other simultaneous builds…or 0 others. The available memory also has to cover the linux instance that runs within the build environment.
Business-level customers can scale to just about any size and length build; we have some running 24Gb builds with a 3 hour timeout (these builds tend to do things like scrape data from several sources and build every page from scratch on sites with >10,000 files).
@zltnvrs, Your suggestion about pricing was not missed and I’ve additionally mentioned it to our sales and marketing teams that set our pricing. They love hearing feedback like that as they make decisions about our future offerings, so please keep it coming!