This is your current bottle neck. Running duel channel is very helpful for overwatch and either high frequency or or latency ram is also helpful. I dont know if 3200Mhz duel channel memory would be enough to get 144hz but its your current best bet. That should allow you to at least reach the limits of that cpu.
Ok so for now go into your settings, turn down fog details to lowest settings, turn off dynamic reflections, turn down shadows to med or low, turn off the bottom two on off lighting settings, restart and see if your fps goes up. For more optimizations and other possible options check out this post.