Complex spreadsheet in Excel 2016 Pro slow but not even taxing the computer

Spreadsheet does scheduling analysis for a manufacturing company. When loading, does database queries and then does not need to do any queries after that. The spreadsheet has a drop down field where the user selects the particular production line (machine) for which the schedule should be analyzed. The cursor turns into the lovely blue rotating circle and chugs away for around 3 minutes or so.

The owner of the company created the spreadsheet and needs much faster performance. We have tried it in 32 and 64 Bit versions of Excel. No real difference.

I have been running this on my laptop which has a Core i7 4800MQ 2.7GHz quad core processor, 16GB RAM, and a 1TB hybrid drive.

I have checked in Resource Manager (Windows 10 Pro 64Bit). The computer is not being bottle-necked in CPU, Memory, Disk or Network. Excel is only using around 12% of the CPU (~98 threads). I went into the power settings on the laptop and set it to the highest performance profile. No real difference. I have made sure that Excel is set to use all CPU cores and hyper-threading.

We looked at the network traffic details in Resource Monitor and noticed that it appears to be communicating across the Internet to Microsoft's servers (did a little research on the various IP addresses to which it is trying to talk and they look to be Office 365 related hosts, even though this is Full Office 2016 Professional and not Office 365). I have done the right mouse click on the Excel.exe line in Resource Monitor and selected Analyze Wait Chain and it indicated that Excel is running normally.

I have turned off the network connections on the PC (pulled Ethernet cable and turned off wireless) and the spreadsheet still works but the performance does not change at all.

We are considering getting a faster PC to run this spreadsheet since it is very important to us. I can pick up a workstation class PC with two physical Xeon CPUs and a ton of CPU cores. But I am not sure that it will make much difference. If I am not running out of CPU resources on my laptop with 4 cores and 4 hyper-threading "CPUs," I am not sure that the spreadsheet will complete its calculations any faster.

Just to provide a little more background on me so you understand I am not a green newbie, I am the IT Manager, with over 20 years of IT experience in systems, desktop and server operating systems, networking, storage, virtualization, etc.

So here are my questions:

Any idea why Excel or Windows 10 is capping its usage of the CPUs around 12% (I briefly saw it it 13% a few times) instead of using more of the CPU resources and finishing the calculating sooner?

Is there any kind of utility that might give more insight into what Excel is doing during the twirling blue circle so we can see if there is a way to streamline the processing within Excel?

I do believe there is some VBA code in the spreadsheet as well. Is there a way to see if the hold-up is on the VBA end?

Any help you provide or advice would be greatly appreciated.

Thanks!!