Can my Early 2015 13 inch MacBook Air that is currently running OS X ElCapitan 10.11.6 be upgraded to Monterey?

short answer, yes.

but, jumping all the way from el capitan directly to monterey may be too big a leap.. officially it should work, but there have been reports of people trying to jump from mojave to monterey has prevented the mac from upgrading. and mojave is much closer to Monterey than el capitan. IMHO, if you have the time, i would step up from el capitan one macOS at a time all the way up to monterey. it will take quite a while, but you will be sure to get all the important components that you may miss out on if you try to leap over all those other macOSes.

you can find all the required downloads here: How to get old versions of macOS - Apple Support

See here.

https://support.apple.com/en-gb/HT212551

Another thing to consider is your apps. 32 bit apps will not work with Monterey and will have to be upgraded or replaced with an alternative. Download and run the free GO64 app to see which of your apps will or will not work with Monterey.

It can be an expensive system upgrade if you have a lot of 32 bit apps that must be upgraded via purchase.