I would suggest you run our Premiere Pro BenchMark (PPBM) which works with CC 2015 (Premiere version 9) and watch your GPU-Z during the exporting of the MPEG2-DVD with GPU and then also the H.264 exporting. These two both have lots of MPE GPU accelerated effects and features.
As Bill stated, run the PPBM benchmark. You should be getting a timed result that's close to 50 seconds for that GTX 750 Ti in the MPEG-2 DVD export portion of the suite, and somewhat faster than the 130-ish second result I had achieved in the H.264 Blu-ray export portion of the suite (my current main PC has only four physical cores plus hyperthreading in the CPU). If either or both results are significantly longer than the numbers that I stated, either your PC isn't optimally tuned or you have a bottleneck somewhere in your PC.
OK. Big thanks for this information. I have run the test and GPU is definitely working.
MPE gain of 1.9 but with 6 core i7 and 750Ti the gain would only be modest. It looks like the problem is with some aspect of the particular Pr project file. Media from the same cameras in a test project with accel effects make the GPU do work, 99% utilisation.
Given that when rendering a timeline with accelerated effect the CPU is at about 30 - 50% and the GPU is at 99% would it be worth considering upgrading the GPU to a better performing one or does it depend on the balance of accelerated to non-accelerated effects in the sequence? I knew when I bought the 750ti it was not going to be very powerful but was a good step up from the previous ATI GPU.
Thanks again for the help, the benchmark was the right tool.
PS UPDATE - Red Giant Denoiser II seems to be the problem. When added to a clip it blocks access to the GPU for all other effects. Just running on it's own makes Pr very slow and unresponsive but it does not crash. Denoiser II says it uses GPU but not on my machine. I will create a ticket with Red Giant and check out Neat Video as well.