Open Activity Monitor and check the usage when you try to do that.
I've seen 2015 15" MBPs slow to a crawl when simply trying to scroll through a large Word document with loads of content -- CPU usage goes to nearly 400%. Also occurs on 2012 cMBP. Issue happens regardless of forcing dGPU or iGPU, so I think Office is set for CPU to render or process everything. Also happens on 2011 & 2016.
TL;DR: Microsoft's programming for Office is really shoddy, so although the problem I've described is different to yours, I wouldn't be surprised if you noticed equally high resource usage when trying to rename an Excel tab.
I really think MS Office Suite for Mac is the worst app I have ever seen. Especially Outlook (current version) is heavily lagging, when it comes to calendar events and reminders I see beach balls all the time... not to mention, that Outlook is completely crashing regularly (no other of my Mac apps does that).
OP, what you've described in the subject is not normal in my experience, however, CPU usage does spike when work is performed in the Page Layout View mode, much less so when working in Normal View mode. If you're using the former View mode, I suggest a switch to Normal View.
I'd read bug reports about this issue as early as last summer. I work in the Windows version of Excel, it too will occasionally peg a GPU or CPU in Page Layout View - I generally only work in Normal View.