Yeah, so that should be plenty to run Excel at any needed level of use. That's a Haswell era i5-4258U and with 8GB of RAM there really shouldn't be much trouble with that. Of course, I don't know how complex your calculations are or what else you might be running on that system, or how well that Windows 7 installation runs on Mac hardware aside from the known factors of the i5 and 8GB of memory, but spec wise you are pretty good.
Are you running 32 or 64 bit Windows 7?
Are you running the Mac or Windows version of Excel?
Are you running 32 or 64 bit Office?
What VERSION of Office (2007, 2010, 2013, etc.)
These things make a difference because if your configuration or software are not allowing you to use more than the ~4GB of a 32 bit system, that will somewhat affect spreadsheet performance. Memory capacity is definitely a factor when you have big documents or a hell of a lot of rows and columns. If you have calculations that are factoring entire rows and columns, or combinations of rows and columns, then CPU performance AND memory are big but even though that is a mobile processor, not as capable as a desktop variant, it should still be really capable with just an office spreadsheet.
If you really just want to do a desktop, which of course WILL be more capable, that is totally up to you and practically ANY desktop platform from the last three or four generations of Intel or any Ryzen 5 or 7 configuration should be more than enough to handle what you are doing so long as you are using a 64 bit OS with 64 bit Office, in order to take advantage of the larger amount of memory. Especially if you are multitasking or running other applications or many browser tabs simultaneously.
There are also some other things you can likely do that will aid in reducing the demands of the spreadsheet and gaining some performance.
I won't go into all those, but suffice to say that there are a lot of things you can do to reduce the footprint of an Excel spreadsheet when it comes to resource demand. Opening a new instance of Excel for EACH spreadsheet is one. Simplifying or actually using BETTER formulas is another.
There are a bunch of things you can do listed here:
https://answers.microsoft.com/en-us/office/forum/office_2010-excel/can-you-suggest-pc-specifications-for-working-with/64fa3b20-28e6-4058-acc2-191cf96df241?auth=1
And I'm sure there are many other potential changes you can make to improve Excel performance to be found at some of these links.
https://www.google.com/search?num=100&safe=active&source=hp&ei=KnuDWrH9A47OjwOzu6iwCQ&q=how+to+increase+performance+in+excel&oq=how+to+increase+performance+in+excel&gs_l=psy-ab.3..0i22i30k1l9.1401.12520.0.12825.37.36.0.0.0.0.140.3429.26j10.36.0..2..0...1.1.64.psy-ab..1.36.3426.0..0j0i131k1.0.Ra5_7PtCZaM