I use an Imac in my office and work with After effects on small sales video jobs - nothing too fancy. I need to get a macbook for my upcoming trips. I am very reluctant to pay for the latest model since the touchpad is not that important for me. I thought I might get a refurbished model. What would be my most suitable configuration to run AE smoothly and render stuff in reasonable amounts of time? Can I get away with a 2015 Macbook pro on 16mb ram?
Well, that's pretty much a non-question. Anything is better than nothing I guess. Everything else too much hinges on the specifics of the projects and what's involved, but frankly if you are using some iMac only, I see no reason to be concerned with much of anything. Sepending on what processor your iMac actually has and from which year it is, even the lowest MacBook Pro might outrun it...
Your system info provided is much too vague, as is the type of footage you are working with, ( what codecs and resolutions, frame rate,etc.).
In any case, AE will use as much system ram as you can throw at it...16GB is too lean...32GB is a minimum. Also, the video card must have at least 4GB of video memory on it, if working with 4K.
In general, a quality newer i7 CPU with 4 cores and 8 threads is the desirable minimum.
Lastly, the speed of your storage is important...if Macbooks have only one drive, make sure it is a fast SSD at minimum, M.2 NVMe PCI SSD would be best. Then, you would need a high speed external drive as well, like a Samsung T3 connected to USB3,or, something which connects to Thunderbolt which actually performs fast.......many don't...watch out !