SketchUp (like all CAD programs) only runs on a single processor, it does not (cannot) multithread. So the number of cores is irrelevant, it still matters for other programs and for doing things on the side while SketchUp is running. GIven that SketchUp is running on one core the main factors effecting lag are: clock speed, ram, hard drive speed, and graphic card.
Clock speed is the basic speed limit of any given processor, the faster the better. 2.2 is low but workable. With turbo boost macs can overclock and run faster but as the processor heats up they throttle back down, especially in laptops. Get the fastest clock speed you can afford.
Ram is good, 16 is workable, 32 or 64 is better. In Mac you get one chance to decide as it is not upgradable, so go big from the beginning. If I were buying today i would go minimum 32.
Hard Drive speed is important for loading and working on big models. Obviously a 100 or 200 gb file is bigger than your ram can hold, so the processor is constantly writing and reading from the harddrive to load and work with bigger files. Solid state drives are becoming the standard and accesses info much quicker than spinning plates. Again, not upgradable, so go big, 1tb min?
SketchUp lives and dies by the graphics card. For instance some low end macbook airs only the integrated graphics card struggle to run it at all. You need a good quality discrete GPU (not integrated card). The good news is that most new MBPs have strong discrete cards (I think some older 13" did not so watch out if you’re goin used), Apples choices are often not the most powerful in the world like some pc gaming laptops, but are tried and true and they tend not to have the constant driver updates that plague the windows systems. Vram, get as much as you can afford, minimum 2gb?
As far as what to choose things are a bit up in the air now with the release of the M1 chip. By all accounts the M1 even running rosetta 2 is blisteringly fast and once SketchUp is ported to M1 (fingers crossed) it looks like it will be the fastest system to own on the planet short of deep blue. There are a couple ways to look at this, either hold out for the M1 MBP which is surely on the way, and take a chance to own your own rocket ship, or wait for the glut of perfectly good high end intel based MBP’s that get dumped on the used marked once the M1 drops and all the kids run to the apple store for the latest thing. Honestly I’m not sure where I stand…
All opinion, your mileage may vary.