Is there nothing else I can do to speed up my rendering?
Short of a new machine, no. 3D rendering is very hard work, and has always required top-of-the-line hardware. This is why desktop Mac Pros with dual GPUs exist. (I'm not saying you need to buy one of the insanely expensive ones, but companies are prepared to pay those prices because time is money.)
A MacBook Air is designed and marketed for 'light-to-moderate' use; and the MacBook Pro name indicates more capable hardware for professional-level work, like video, software development and animation. An Air wasn't the right tool, even in 2015! ;-)
If you're doing this commercially, then I'd suggest investing in a new M1 Pro or Max MBP. The GPU capabilities of those Macs holds up well against current desktop GPUs, and the overall performance is absurdly fast.
If you're doing this as a hobby, and can't afford to spring for a new MBP, then I'm afraid you'll just have to let it run. It will get hot, but the fans are designed to cool things down, and the CPU will also slow down as it gets hotter; in extremis the CPU will shut itself off to prevent heat damage if things get out of control. However, you'll be 'pushing the envelope', and something might possible 'give', if you are doing this a lot.
In the old days, people would leave these sorts of tasks running overnight!
One more thing: Apple's laptops between 2015 and the current M1s are 'not great' for a variety of reasons, mostly involving heat, GPUs and bad keyboards, so I wouldn't buy a second-hand Mac laptop in that range either.