...you may have not assigned the memory correctly under "settings" in PPro. Ideally, I have read that a minimum of 3GB of memory per "thread" is needed by PPro...which in your case would be 12GB assigned to PPro and 4GB assigned for "other uses"
Also, Windows "power settings" must always be set to "maximum performance", as the DEFAULT settings may throttle the laptop even when plugged in. I experienced this with a new laptop once....of course, any laptop MUST be plugged in while editing or exporting or the machine will "throttle" no matter what the power setttings are.
The single stick of memory was GIMPING your machine...it obviously was easily maxxed out and thus became an overloaded "bottleneck". If it works "ok" for now, don't worry about it....its really not worth upgrading anything with the inferior CPU and GPU.
If you ever get serious in editing and MUST be limited to a laptop, look to the newer and faster gaming laptops which have :
1. i7 - 7700 Kaby Lake intel CPU 4 core/8 threads
2. minimum NVidia 1060 GPU w 6GB video memory...( 1070 much better )
3. 32 GB system memory
4 M.2 PCI Gen. 3 x 4 lanes slot for connecting a Samsung 960 Pro PCI NVMe SSD for absolute fastest speed, ( 3GB / sec read, 2GB sec write). With a 1TB version of this SSD, separate drives are no longer need...everything can just go on it.
5. minmum 17.3 inch 1080p display, preferrably IPS.....higher resolution not needed at this small size....pixel density is fine.
6. High speed external ports for connecting high speed external drives ,or, larger external monitors. ( I currently have TWO 1440p IPS monitors running at full resolution at 60fps on my laptop for a total of 3 screens with NO problem ! ).