The problem isn't the technology here. The problem is that they were using a replica of the OLTP database for reporting purposes. OLTP and OLAP are hugely diff

The problem isn't the technology here. The problem is that they were using a replica of the OLTP database for reporting purposes. OLTP and OLAP are hugely different workloads. A good 3NF (or close to it) schema that you'll find in an OLTP database is designed for fast writes with minimal locking; it fits well with the workload of OLTP. If you're reporting on that data and performing analytical queries, then your schema needs to reflect that and optimize for large reads without much concern around lock contention for the primary workload. I am not opposing the suggestion of a columnstore database, as we utilize these extensively with our clients. There is simply a much larger problem in the specified example. 15B rows is not too big a deal in an RDBMS for an analytical workload.