To know how much of a boost you would get I would suggest searching for benchmark results from other users with a similar setup and work as you that upgraded the RAM.
RAM and SSD are huge boosts to performance, I just discovered that with my 2011 MacBook Pro (doubled the RAM and installed a SSD).
What I also frequently found when looking for the RAM is that the highest the better for video editing and having friends working in that field too, 16gb is the minimal amount apparently so I would suggest boosting the RAM and then buying the new Mac maybe, depends on your budget and the price of the RAM you specifically need. Maybe the upgrade in RAM won't be that expensive and a good trade-off while waiting for the new Mac purchase. You have to see for yourself.
I don't want to make any advertisement but the brand Crucial has come recommended on many sites and communities online for Macs. Of course you should do your own research and decide what suits you best.
I also got my SSD and RAM from them.
Also on their site you can either choose your model or use their system scanner to precisely identify the RAM and SSD upgrades that are right for your precise model, with prices.
Also if you decide to put an SSD in addition to the RAM, the PCI version as opposed to the SATA ones are supposedly much faster since the PCI port is faster than the SATA, therefore for video editing that would be good I suppose.
Just my 2 cents, hope it helps !