Maybe. I've heard that the processors in some Roku TVs are pretty limited. Of course, whatever issue you have now may be limited by the current Roku TV, or your network speed (which in turn could be a limitation of your internet plan or your Wi-Fi.)
A Roku Ultra should be the "best" ie: fastest processor, most memory, best Wi-Fi radio and option to connect with ethernet which is usually better than any Wi-Fi. On the other hand, even with a Roku Express (which might still be better/faster than what's in a TV) I never see any issues. (I only stream HD/1080. For 4K you would need something better than an Express.)
