I have thought about getting a new battery but not upgrading my storage. It is something I would consider
Ultimately it is up to you to decide whether or not it's worth upgrading. I am not impressed with the direction Apple is taking with their limiting our ability as owners of our own computers to either upgrade or repair them. Once you purchase the computer it is yours. In my opinion we, as owners of our own computers, should have the right to repair or upgrade them however Apple does not agree and as such, I would rather have computers that I can still repair and/or upgrade.
Buying the new M1 processor laptops, you will find there are absolutely no upgrade paths for them and like the current iPhones, you will find out that you won't be able to repair them as well. What you buy is what you will have to put up with whereas with your 2015, you still have options. I think for your usage, what you will find is that by upgrading your storage drive (getting a Sintech adapter and a decent NVMe M.2 storage drive as well as a new battery which is very easy to replace in the 2015 MacBook Air) you will find that the performance of your laptop to be more than adequate to do the job for you but that is my opinion.
Here is a link to a Sintech adapter on eBay ($19.08 with free shipping - you need the Sintech adapter to install the NVMe storage drive):
M.2 SSD Adapter Card Macbook SSD Adapter Card U.2 SFF-8639 SSD Adapter Card mSATA Adapter Card mPCIe/X1/UX31 SSD Adapter Card ZIF HDD Adapter Card. Date First Available: September 18, 2016. Color: M2 for Upgrade Mac.
www.ebay.com
and a Samsung 970 EVO NVMe M.2 Storage drive...
500GB ($77.95 with free shipping):
https://www.ebay.com/itm/Samsung-97...519371&hash=item217913b9e2:g:6YgAAOSwz0xfdedI
1TB ($139.95 with free shipping):
https://www.ebay.com/itm/Samsung-97...658294&hash=item217f412cf3:g:wqwAAOSwVrNfxnmr
The battery I would source from the iFixit web site:
MacBook Air parts for DIY repair. Batteries, displays and small parts all tested and guaranteed with fast shipping and easy returns.
www.ifixit.com
One more thing.... Audit13 has good recommendations for other NVMe storage drive options that are not as power hungry as the Samsung drives are. Reach out to him for recommendations. He also has good inputs in this area.
