It can be upgraded to Monterey macOS12.X but no later. See the following from Identify your MacBook Air model - Apple Support
MacBook Air (13-inch, Early 2015)
Model Identifier: MacBookAir7,2
Part Numbers: MJVE2xx/A, MJVG2xx/A, MMGF2xx/A, MMGG2xx/A
Newest compatible operating system: macOS Monterey
MacBook Air (11-inch, Early 2015)
Model Identifier: MacBookAir7,1
Part Numbers: MJVM2xx/A, MJVP2xx/A
Newest compatible operating system: macOS Monterey
Also see: How to download and install macOS - Apple Support
Be aware that if you upgrade to Catalina 10.15 or later you will also need to update any non-Apple 32-bit apps. See: https://www.stclairsoft.com/Go64/
or
https://www.macworld.com/article/232735/how-to-check-if-mac-software-is-32-or-64-bit.html