I suspect there are no hardware issues with your MacBook Air**.
As others have pointed out, it's eight years old, and you've gotten years of great value from your initial investment!
It was more than adequate in 2015 as a durable, light, very portable Mac and was well-provisioned to run Mac OS X Yosemite and 2015-era apps. Unfortunately, that level of performance is no longer adequate when running 2020's-era macOS Monterey and 2020's-era apps.
So you might avoid a separate trip to the Apple store only to find out they can find nothing wrong with your MacBook Air. If you are definitely going to purchase a new iMac or other Mac very soon, I would schedule a single appointment to purchase the new Mac and arrange to have the store transfer your files from your Air to your new computer in a single visit.
Dropping into GeekBench computer benchmark jargon, the least-capable iMac 24" Apple Silicon M1 8-core/7-core processor offers nearly 3-times the single-core benchmark performance of your 2015 dual-core Intel i5, 1711 vs 611, and almost 6-times the multi-core benchmark performance, 7469 vs 1258.
Performance benchmarks are only one measure of real-life computing power, and may not adequately represent the performance a user will actually experience. Before making your purchase decision, ask your Apple rep to let you try out one of the demo units in the store, configured exactly the way you intend to buy it, and using the actual apps you intend to use.
** I also own a 2015 13.3" MacBook Air with 8GB RAM, 256GB SSD, and 1.6Ghz dual-core Intel i5 processor.
I still use mine as a bedside computer for reading e-books, and not much else, with virtually no portable use. It's still running macOS Catalina, and Catalina still offers adequate performance and security for my very limited purposes, never going online. So I've intentionally ignored the System Preferences notices to update to macOS Monterey.