For the most part, only thing native AE uses the GPU for is the obsolete ray-traced renderer. Very few people use that feature, so I wouldn't worry about it. More details here: GPU (CUDA, OpenGL) features in After Effects CS6 and After Effects CC
Some third-party plugins do use the GPU, but their requirements are completely separate from those of the outmoded ray-traced renderer, so check what the requirements are for any third-party plugins you plan to use.
If you did want to use the ray-traced renderer (why?!?), you should look at getting a different GPU or choosing a third-party alternative.
If you do upgrade to CC, it won't help the ray-traced renderer use your GPU because that GPU can never accelerate that effect (it was only a narrow set of NVIDIA cards - and the latest round of NVIDIA cards can't even do it). But you DO get Cinema 4D Lite for free with CC, so that's nice. It's way more powerful. Make sure, when you install CC that you choose the option to keep your old version of AE: keeping previous versions installed when installing CC 2015 applications . And, consider installing CC 2014 as well as CC 2015 since some people are having issues with CC 2015 (at least until the bug-fix update comes out in a couple of weeks). How to Find and Install Previous Version of Adobe Apps in CC 2015