Hi, @zltnvrs. There is additional time allowed for post-processing and uploads. This is likely the reason for timeouts happening in 30 minutes instead of 15.
For additional build resources (for example, longer build times) a Business tier plan is required. <- Edited on 2020-10-27 as this has changed and hasn’t been true for some time.
Regarding the RAM and CPU available in the build image, I am hoping someone else here at Netlify can answer that question.